| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
From the Institute of Pathology, Case Western Reserve University, School of Medicine, Cleveland, Ohio.
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
-carboxymethyl-L-lysine (CML), has an
EDTA-like structure, which may predispose it to bind redox active
copper. METHODS. Young, old, and cataractous human lens protein fractions were glycated with ascorbic acid and tested for their ability to bind Cu(II) by atomic absorption spectroscopy and oxidize (14C1)-ascorbate by radiometric thin-layer chromatography method. AGEs were assayed by high-performance liquid chromatography (HPLC). CML-rich proteins were immunoprecipitated from young, old, and cataractous crystallins using affinity-purified CML antibody and tested for their ability to oxidize ascorbate and generate hydroxyl radicals in the presence of H2O2 using 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) spin-trap and EPR spectroscopy.
RESULTS. Ascorbate oxidizing activity at 24 hours of native crystallins was significantly increased in both the water soluble (WS; P < 0.001) and insoluble (WIS; P < 0.05) fractions from cataractous and normal lenses. The chelator DTPA completely prevented oxidation up to 24 hours of incubation but less effectively thereafter. Mean endogenous Cu content in pooled young, old, and cataract fractions increased from 0.016 to 0.026 nmol/mg protein, respectively, in WS (P < 0.05) and WIS (P < 0.001) fractions, and Cu(II) binding was 20% to 30% increased in cataractous versus old and young lenses in WS (P < 0.01) and WIS (P < 0.001) fractions. Mean levels of the AGEs, CML, and pentosidine were markedly elevated in WS and WIS fractions from cataractous versus old or young crystallins (20% to severalfold, P < 0.05 to P < 0.001). In a separate experiment, protein-bound Fe was not elevated. Crystallins ascorbylated in vitro showed an increase in CML as well as Cu(II) binding. CML-rich proteins (immunoprecipitated from cataractous lenses) oxidized ascorbate ~4 times faster than similar proteins from young and old normal lenses (P < 0.01) and generated hydroxyl radicals in the presence of H2O2 and DMPO.
CONCLUSIONS. The association between CML formation, copper binding, and generation of free radicals by cataractous lens crystallins can be duplicated by ascorbylation in vitro. These effects are only in part attributable to CML itself, and other modifications (AGEs, conformational changes) may participate in the process. A vicious cycle between AGE formation, lipoxidation, and metal binding may exist in the aging lens, suggesting that chelation therapy could be beneficial in delaying cataractogenesis.
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
Among possible mechanisms, considerable evidence has accumulated in
support of the Maillard reaction (i.e., the reaction that leads to the
formation of advanced glycation end products [AGEs] and protein
cross-links). It is now well recognized that the Maillard reaction does
not need to be initiated by glucose but rather can also be initiated by
oxoaldehydes such as methylglyoxal.13
14
In addition,
there is evidence that suggests ascorbate may be a more important
modifier of lens crystallins than glucose, because the modification
rate by ascorbate is much faster than that of glucose at equivalent
concentrations.15
To date, close to 10 AGEs and
cross-links have been discovered in the human lens besides glycated
lysine itself. They include the following:
N-(carboxymethyl)-L-lysine (CML),
pentosidine, fluorophore LM-1, pyrraline,
N-carboxyethyl-lysine (CEL), methyl
glyoxal lysine dimer (MOLD)/imidazolysine, glyoxal lysine dimer (GOLD),
argpyrimidine, and oxalic acid monoamide (OMA).16
17
18
19
20
21
22
23
24
Although there is strong evidence that amino-carbonyl reactions of the Maillard type are involved in the aging process of lens crystallins, recent evidence also suggests that purely oxidative modifications of lens crystallins occur in aging. This has been demonstrated by the accumulation of hydroxylated amino acids.25 Although some of these oxidation reactions could be of photooxidative nature and involve singlet oxygen (1O2) or superoxide anion, the formation of most hydroxylated amino acids cannot occur without a metal catalyst such as copper. Presence of the latter was indeed found to be increased in old and cataractous lenses in most, although not all, studies.26 27 28 29 30
In a preliminary study, we found that the rate of spontaneous ascorbate oxidation increases in the presence of old and pigmented cataractous versus young human lens crystallins,31 thus raising the question of the mechanism by which this oxidation process is catalyzed in the aging lens. Here we hypothesized, based on our recent finding of a structural analogy between the major AGE CML and EDTA,32 that AGE formation in lens crystallins leads to binding of redox active copper. We present below evidence that strongly suggests a close relationship between CML formation and copper-catalyzed ascorbate oxidation by lens crystallins modified by AGEs in vitro and lens crystallins from old and cataractous human lenses.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
Lens Crystallin Preparations
All solvents, solutions, buffers, and dialysis buffers used
throughout this work were treated with Chelex 100 according to
manufacturer’s instructions to prevent artificial enrichment of
protein solutions with transition metals. Human lenses of various ages
and pigmentation were divided into three groups (young, 10–25 years;
old, 65–80 years; and cataractous, 75–90 years) and classified
according to degree and pattern of pigmentation into type IV and
brunescent according to the system of Pirie.1
Each group
comprised pools of 12 lenses each. Lenses were homogenized with
metal-free 100 mM sodium phosphate buffer (pH, 7.4). The homogenate was
centrifuged at 30,000g for 30 minutes, and the resultant
supernatant and pellet were separated. The pellet was suspended in 1 ml
homogenization buffer and centrifuged as above. The two supernatant
fractions were pooled and dialyzed twice against 10 mM phosphate buffer
for 24 hours. The dialysates were centrifuged, and the clear
supernatants were designated as water soluble (WS) fraction. The water
insoluble (WIS) pellet was resuspended in buffer and sonicated in ice
for 5 minutes as previously described.33
The solubilized
protein was recovered after centrifugation at 30,000g,
resuspended, and sonicated again. The second supernatant was combined
with the first and designated as the water insoluble sonicated
supernatant (WISS).
Binding of Copper to Crystallins
Copper binding experiments were performed by reverse dialysis. The
protein solutions (~5 mg/ml) were packed in dialysis membranes and
incubated in a beaker with freshly prepared 500 µM
CuCl2 in 50 mM Tris–HCl (pH, 7.4). After 6 hours
at room temperature, excess free metal was removed by dialysis at 4°C
against a 3-l buffer for 3 days with 2 to 3 buffer changes at 4°C.
Copper content in the crystallin solutions was quantified by atomic
absorption spectrophotometry (atomic absorption spectrophotometer model
2280; Perkin–Elmer, Foster City, CA) using homemade standards
in buffer.
Acid Hydrolysis of Proteins
Crystallin protein fractions were hydrolyzed with 6N HCl for 18
hours at 110°C. Hydrolysates were dried and taken up in an aqueous
solution of 0.01 M heptafluorobutyric acid for pentosidine and CML
assay by HPLC. Total amino acid concentration estimation in the
hydrolysate of insoluble crystallins was determined using
L-leucine as standard as described
previously.18
HPLC Assay for
N-(Carboxymethyl)-L-Lysine
CML was assayed in the protein acid hydrolysate using the
o-phthaldialdehyde (OPA) method and post-column
derivatization as previously described,34
with some
modifications. Briefly, CML-containing fractions were isolated using
system 1 consisting of water (eluent A) and 60% acetonitrile in water
(eluent B) both with 0.01 M heptafluorobutyric acid (Aldrich),
reverse-phase C18 column (0.4 x 25 cm, 5 µM), Vydac
218TP54, flow rate 1 ml/min. Gradient was 2% B for 20 minutes,
followed by 2 minutes to 100% B. The collected CML-rich fractions were
analyzed by OPA method using system 2. Column and flow were as for
system 1, with 5% propanol (eluent A) and 60% propanol in
H2O (eluent B), both with 3 g of sodium
dodecyl sulfate (SDS) and 1 g of monobasic sodium phosphate
monohydrate/l adjusted to pH 2.8 with phosphoric acid. The gradient was
15% B to 22% B in 30 minutes, and 22% to 100% B in 5 minutes.
HPLC Assay for Pentosidine
Pentosidine in the protein hydrolysate was quantified by combined
reverse-phase and cation-exchange HPLC as described by Odetti et
al.35
Approximately 10 µmol (leucine equivalent) of
crystallins was injected into a C18 reverse-phase column (Vydac 218TP,
0.46 x 25 cm, 10 µm) and eluted from 0 to 35 minutes with a
linear gradient of 10% to 16.8% acetonitrile from 0 to 35 minutes in
water and 0.01 M heptafluorobutyric acid (HFBA). Eluate
containing pentosidine was collected, dried in a Speed Vac concentrator
(Savant Instruments, Hicksville, NY), and reconstituted in 200 µl of
0.02 M sodium acetate buffer, and 125 µl was injected into a
cation-exchange column (Water Protein Pak SP 5PW, 7.5 x 75 mm).
Elution of pentosidine was achieved by using a gradient of 0 to 0.06 M
NaCl over a period of 40 minutes. Pentosidine was quantified with a
fluorescence detector by comparing peak areas with those of the
standards.
Preparation of Ascorbylated Crystallins
Ascorbylated crystallins were prepared by incubating normal
crystallins (15 mg/ml) with various concentrations of ascorbic acid
(0.5, 5, and 20 mM) in 100 mM phosphate buffered saline (PBS)
(pH, 7.4) for a period of 1, 2, 4, and 30 days. All the incubations
were carried out in the dark and under sterile conditions. At the end
of the incubation period, all reaction mixtures were extensively
dialyzed (twice overnight) against either non–Chelex-treated phosphate
buffer to remove the reactants, but not the transition metals that
would bind to the AGEs, or the native protein. The solutions were
stored in polypropylene tubes at -80°C.
Ascorbate Oxidation Assay
Ascorbate oxidation assay was performed as previously
described.31
The reaction volume of 300 µl consisted of
protein (3 mg/ml) with 2.0 mM of
14C1-ascorbate (1.25
mCi/mmol) in Chelex-treated 100 mM Na/PO buffer (pH 7.4) with and
without 1 mM DTPA. The incubation was performed at 37°C in the dark,
with mild rotary shaking. Aliquots were withdrawn at various time
intervals, mixed immediately with cold 4% metaphosphoric acid
containing 1 mM DTPA, and centrifuged at 10,000g for 1
minute, and the protein-free supernatants were spotted immediately
under N2 and analyzed for ASA degradation
products by TLC. The peaks were identified by comparison to known
standards and quantified by determining the distribution of
radioactivity using a Berthold (Wildbad, Germany)
radioactivity scanner (type LB 2852). TLC was performed on silica gel
reverse-phase plates (catalog No. 4809–820; Alltech) with a solvent
system comprised of acetonitrile–water–acetone–glacial acetic acid
(80:15:5:2).
Preparation of Affinity-Purified CML Antibody
A polyclonal CML antiserum from a 6-week-old New Zealand white
rabbit immunized with carboxymethylated Keyhole Limpet Hemocyanin
prepared as described by Reddy et al.36
For purification
by affinity chromatography the polyclonal antiserum (15 ml) was mixed
with saturated
(NH4)2SO4
(1:1 vol/vol) and incubated at 4°C for 6 hours. The mixture was
centrifuged at 3000g for 15 minutes, and the pellet was
reconstituted in 30 ml of 50 mM Tris–HCl (pH, 7.4).
A CML–Sepharose affinity column was prepared by reacting ~5 g L-lysine Sepharose (catalog No. L-6132; Sigma) swollen in 50 ml of PBS with 25 mM glyoxylic acid and 25 mM of NaCNBH3 in PBS so as to make a total volume of 75 ml. The mixture was incubated at 37°C overnight with mild rotary shaking. Thereafter, the gel was extensively washed with PBS, packed in a column (Bio-Rad, 2.5 cm x 7 cm), and equilibrated in 50 mM Tris–HCl (pH, 7.4).
Reconstituted (NH4)2SO4 precipitated serum sample (30 ml) was passed over the CML–Sepharose column and allowed to sit for ~30 minutes. The column was washed until the absorbance at 280 nm reached zero (approximately 40 ml). The bound antibody fraction was eluted with 100 mM glycine/HCl buffer (pH, 2.5) containing 150 mM NaCl. The eluent was collected in tubes containing 0.5 ml of 1 M Tris–HCl (pH, 8.0) to immediately neutralize the pH. The collected eluent was adjusted to a pH of 7.4, dialyzed against 50 mM Tris–HCl (pH, 7.4) for 24 hours with one change of buffer, and concentrated to ~0.8 ml by Centriprep (10,000 cutoff) from Amicon (Beverly, MA). The purity and activity of the affinity-purified antibody was analyzed by SDS–polyacrylamide gel electrophoresis and by direct enzyme-linked immunosorbent assay (ELISA), respectively. The ELISA showed antibody binding was completely inhibited by 3 different CML-rich proteins, by bovine serum albumin modified with glyoxylic acid but not glycolaldehyde under reductive alkylation with NaCNBH3 (data not shown). Thus, the antibody was highly specific for CML.
Immunoprecipitation of CML-Rich Lens Proteins
To water-soluble crystallins (0.4 mg/200 µl) from normal young,
normal old, and cataractous lenses were added 50 µl of
affinity-purified anti-CML antibody, and the mixture was allowed to
incubate for 3 hours at room temperature. Thereafter, 175 µl of the
wet slurry of Protein A–Sepharose CL-4B was added, followed by
incubation at 4°C for another 3 to 4 hours. The mixture was
centrifuged, and the pellet was washed once with dilution buffer and
three times with 20 mM Tris–HCl (pH, 7.4) and 150 mM NaCl. Glycine
buffer (pH, 2.5) with 150 mM NaCl was used to elute the
antigen–antibody complex that was collected by centrifugation after
removal of Protein A–Sepharose by centrifugation. The
immunoprecipitated protein was analyzed for protein concentration, CML
content, and ascorbate oxidizability. For the latter experiment, 75
µl of 0.1 M glycine buffer (pH, 2.5)–containing Chelex-treated NaCl
(150 mM) was added to the precipitate to release the crystallins.
Detection of Hydroxyl Radical Formation by CML-Rich
Cataractous Human Lens Crystallins
The ability of CML-rich crystallins from cataractous lenses to
generate free radicals in the presence of
H2O2 was evaluated using
the modified protocol of Buettner et al.37
The final
incubation mixture consisted of Chelex-treated 50 mM sodium phosphate
buffer (pH, 7.4) with, or without, either CuCl2
(0.5 mM) or the CML-rich immunoprecipitated crystallins (0.5 mg/ml)
prepared as described above, 80 mM
5,5'-dimethyl-1-pyrroline-N-oxide (DMPO; with or without 1
mM DTPA), and 0.5 mM H2O2
in a total volume of 0.490 ml. The reaction was started by the addition
of 10 µl of 25 mM H2O2
and the EPR spectrum was recorded after 8 minutes at room temperature
with a Varian Century model Series E instrument. The settings were as
follows: scan range 2 x 102 G, time
constant 2.5 seconds, modulation amplitude 4.0 G, gain 2 x
104, microwave power 12.5 mW, and microwave
frequency 9.44 GHz.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
|
|
AGE Content of Pigmented Cataractous Lens Crystallins
Taken together, the data shown in Figures 1
and 2
suggested a
possible relationship between the degree of crystallin pigmentation,
the extent of Cu binding, and the ability of crystallins to oxidize
ascorbate.
To investigate the role of AGEs in this process, a series of experiments were carried out. First, we determined the levels of the two advanced glycation and glycoxidation products pentosidine and CML. CML levels in the young, old normal, and cataractous protein fractions were 1.4 ± 0.2, 2.3 ± 0.5, and 4.4 ± 0.6 nmol/mg protein in WS fractions and 0.8 ± 0.2, 2.9 ± 0.3, and 6.2 ± 0.5 nmol/mg protein in WISS fractions, respectively. Pentosidine values were 0.2 ± 0.05, 0.4 ± 0.1, and 3.3 ± 0.6 pmol/mg in WS fractions, and 1.3 ± 0.4, 1.5 ± 0.4, and 3.2 ± 0.5 pmol/mg protein in WISS fractions, respectively. Thus, compared with young lens, the cataractous lens proteins showed ~15-fold (P < 0.001) and ~threefold (P < 0.05) increases in pentosidine levels, and CML levels were similarly (~3.5-fold, P < 0.01; and 6-fold, P < 0.001) increased in the WS and WISS fractions, respectively. We and others previously reported similar data.17 40 41
Effects of Ascorbylation of Human Crystallins on Copper
Binding
The results noted above suggested that the increased oxidizing
effect of pigmented crystallins could be related to the presence of
AGEs. To investigate this hypothesis, we evaluated the ability of lens
crystallins to oxidize ascorbate on glycation up to 30 days under
aerobic conditions, with increasing concentrations of ascorbate (0,
0.5, 5, and 20 mM). Figure 3
shows that within 1 to 2 days ascorbate-modified protein oxidized more
ascorbate than at time 0, suggesting that incubation alone may be
exposing redox active sites. Importantly, however, not only was the
extent of oxidation related to the concentration of ascorbate and
partially suppressible with DTPA, but the ascorbate concentration
required to induce these effects was near physiological concentration
(i.e., 1–2 mM in the human lens). Interestingly, on prolonged
incubation (30 days) the protective effect of DTPA on ascorbate
oxidation by the AGE proteins waned, suggesting thereby that the
heavily modified proteins behave similarly to the cataractous lens
crystallins in which ascorbate oxidation was only partially
suppressible by DTPA (see Fig. 1
). The inability of DTPA to completely
prevent oxidation at day 30 (Fig. 3)
may be explained either by the
inability of DTPA to remove the CML-bound metal (Cu or Fe) because of
excessive cross-linking associated with long-term glycated crystallins,
or because ascorbate oxidation was not transition metal dependent.
|
|
|
|
|
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
Carboxymethyl-Lysine as a Ligand for Redox Active Copper in the
Lens
While this article was under editorial review, a related study by
Ortwerth and James42
showed that the addition of calf lens
proteins to a mixture of copper and ascorbate completely suppresses its
oxidation and free radical generation, leading to the conclusion that
"copper, even though it is increased in cataracts, would be strongly
bound by lens proteins, where it cannot function in the oxidation of
sugars." Paradoxically, however, the two studies are not in
contradiction! We too made the identical observation (not shown) that
the addition of human lens proteins to a protein-free solution
consisting of Cu2+ and ascorbate suppresses
oxidative processes. Similar data were reported previously for
albumin43
44
and are in principle applicable to any
protein whereby Cu2+ likely binds to the
glyceryl structure of the peptide backbone.
What, thus, is the relevance of our observations to the oxidative processes in the aging lens? From the data in Figure 4 , it is apparent that CML content at the highest ascorbate concentration used for in vitro ascorbylation was approximately 2.4 nmol/mg protein. However, because the increase in Cu bound was 30 nmol/mg protein, at most 10% of binding can be attributed to CML itself, and, thus, 90% of the copper was obviously bound to other sites, such as the peptide backbone. By contrast, in cataracts there was 1000-fold less Cu2+. However, there was an inverse stoichiometric ratio of 20 to 40 mol CML per mole of Cu, which suggests that some of these sites may indeed serve to bind Cu2+.
Compared with a protein-free system, in which ascorbate oxidation occurs within minutes, the oxidizing activity of the human lens crystallins was slow and extended over several hours. It could thus be argued that it is not a relevant process. However, more ascorbate was oxidized than could be accounted for based on the stoichiometric amount of bound copper. Thus, either the oxidizing activity was due to other transition metals, such as iron, or whatever copper is bound must in part be capable of redox cycling, as recently demonstrated by us.32 Such mechanism(s) could contribute to lipid peroxidation in cataracts, whereby a vicious cycle could exist32 in which CML–protein–metal complexes oxidize lipids and release glycolaldehyde, which itself is a CML precursor.45 In that sense CML is a "molecular sink" for catabolites and processes that are insufficiently detoxified by the old and cataractous lenses.
Other AGEs that May Bind Metals in the Lens
Other ligands, besides CML, may conceivably form coordination
sites for redox active metals. For example, methylglyoxal is the
precursor of CEL, a molecule which has structural homology with CML. It
is the second most abundant modification in the aging human lens next
to CML.20
Thus, this EDTA-like modification should also
have metal-binding properties. Furthermore, whereas CML has been found
to form in the lens and from ascorbate by several
groups,16
46
47
Pischetsrieder et al. discovered a novel
modification resulting from protein ascorbylation (i.e.,
OMA).48
Immunoreactive OMA was recently detected in aging
and cataractous crystallins.24
Of interest is the fact
that this modification also has a carboxylic group, which could
conceivably serve as a coordination site for transition metals.
There are several sites in human lens crystallins where suitable coordination sites for metal binding to CML-modified lysines might exist. Such sites are rich in histidine and glutamic acid residues. For example, potential copper-binding sequences in human ßA3-crystallins include 121HKE123, 129EKE131, and 192YKHW195. In the latter sequence, the proximity of tyrosine and tryptophan may lead to "in situ" metal-catalyzed oxidation of these residues. In human ßB3-crystallins, lysine is found in a histidine-rich sequence: 113HHKLH117.
Nature of the Redox Activity of Cataractous Crystallins
The data presented above implicate transition metals in ascorbate
oxidation, whereby the precise extent to which Cu(II) or Fe(III) are
involved, both in the in vitro ascorbylated samples (Fig. 4)
and in the
cataractous crystallins (Figs. 5
6
7)
, remains to be determined.
Indeed, the fact that mean Fe levels were identical in each group
suggests, but does not prove, that Fe is not the redox active element,
because Fe can be bound in redox active as well as redox inactive
states. However, the inability of DTPA to completely prevent the
oxidation of ascorbate suggests that other mechanisms of ascorbate
oxidation are also operational. Because the degradation of ascorbate
occurred in the incubator, in the absence of light, photooxidative
destruction, as proposed by Linetsky et al.,49
is
unlikely. However, a recent study by Lee et al. points to the existence
of non–metal-catalyzed oxidation of ascorbate by
methylglyoxal-modified protein, which mimics metal-catalyzed
oxidation.50
Such mechanism is very attractive in light of
the recent work implicating methylglyoxal in lenticular
aging.14
The data presented above and the data existing in the literature show that there are several modifications and mechanisms, in addition to CML, that could explain the redox activity of cataractous crystallins. Evidently, the single major element needed for oxidation to occur is O2. Eaton51 has pointed out that the lens should be considered "canned" (i.e., it protects itself from oxidation by having a very low O2 tension, especially toward the nucleus). Indeed, exposure of whole animals to hyperbaric oxygen can induce cataracts.52 However, even the concept that O2 is necessary for oxidation to occur is challenged by Lee et al., who were able to reduce ferricytochrome c in absence of O2 with methylglyoxal Schiff base protein adduct.50
Based on the many observations showing that lens crystallin modifications by oxidative processes and carbonyl agents are dramatically increased in age-matched cataractous versus non-cataractous lenses, it is not difficult to speculate that a breakdown of the permeability barrier of the fiber cell must be a key event in cataractogenesis. Indeed, in previous experiments in which we exposed rat lens crystallins to high galactose stress in vitro or in vivo, we found the permeability barrier to 2,3-diketogulonate completely lost.36 This resulted in accelerated ascorbylation of the crystallins on exposure of the lens to 14C-ascorbate.
|
Conclusions |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
|
Acknowledgements |
|---|
|
Footnotes |
|---|
Submitted for publication April 26, 1999; revised September 3 and December 1, 1999; accepted December 9, 1999.
Commercial relationships policy: N.
Corresponding author: Vincent M. Monnier, Institute of Pathology, Case Western Reserve University, 2085 Adelbert Road, Cleveland, OH 44106. vmm3{at}po.cwru.edu
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionConclusionsReferences |
|---|
-(carboxyethyl)lysine, a product of the chemical modification of proteins by methylglyoxal, increases with age in human lens proteins Biochem J 324,565-570
-aminolysine residues J Biol Chem 271,19338-19345-(carboxymethyl)lysine is a dominant advanced glycation end product (AGE) antigen in tissue proteins Biochemistry 34,10872-10878[Medline][Order article via Infotrieve]
-(carboxymethyl)lysine and N-(carboxymethyl)hydroxylysine in human skin collagen Biochemistry 30,1205-1210[Medline][Order article via Infotrieve]
-(carboxymethyl)lysine, is a product of both lipid peroxidation and glycoxidation reactions J Biol Chem 271,9982-9986-(carboxymethyl)lysine formation in lens proteins and polylysine by autoxidation products of ascorbic acid Biochim Biophys Acta 1117,199-206[Medline][Order article via Infotrieve]
This article has been cited by other articles:
|
|
 |
|
  S. M. Culbertson, E. I. Vassilenko, L. D. Morrison, and Keith. U. Ingold Paradoxical Impact of Antioxidants on Post-Amadori Glycoxidation: COUNTERINTUITIVE INCREASE IN THE YIELDS OF PENTOSIDINE AND N{epsilon}-CARBOXYMETHYLLYSINE USING A NOVEL MULTIFUNCTIONAL PYRIDOXAMINE DERIVATIVE J. Biol. Chem., October 3, 2003; 278(40): 38384 - 38394. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. J. Padayatty, A. Katz, Y. Wang, P. Eck, O. Kwon, J.-H. Lee, S. Chen, C. Corpe, A. Dutta, S. K Dutta, et al. Vitamin C as an Antioxidant: Evaluation of Its Role in Disease Prevention J. Am. Coll. Nutr., February 1, 2003; 22(1): 18 - 35. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Miyata, C. van Ypersele de Strihou, Y. Ueda, K. Ichimori, R. Inagi, H. Onogi, N. Ishikawa, M. Nangaku, and K. Kurokawa Angiotensin II Receptor Antagonists and Angiotensin-Converting Enzyme Inhibitors Lower In Vitro the Formation of Advanced Glycation End Products: Biochemical Mechanisms J. Am. Soc. Nephrol., October 1, 2002; 13(10): 2478 - 2487. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. W STITT Advanced glycation: an important pathological event in diabetic and age related ocular disease Br. J. Ophthalmol., June 1, 2001; 85(6): 746 - 753. [Full Text] [PDF]
|
|
|
|
|
|
P. Chellan and R. H. Nagaraj Early Glycation Products Produce Pentosidine Cross-links on Native Proteins. NOVEL MECHANISM OF PENTOSIDINE FORMATION AND PROPAGATION OF GLYCATION J. Biol. Chem., February 2, 2001; 276(6): 3895 - 3903. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
