ascorbic-acid and sodium-cyanoborohydride

The autoxidation of ascorbic acid (ASA) leads to the formation of compounds which are capable of glycating and crosslinking proteins in vitro. When the soluble crystallins from bovine lens were incubated with ASA in the presence of sodium cyanoborohydride, a single major adduct was observed, whose appearance correlated with the loss of lysine. When polylysine was reacted with equivalent amounts of ASA under the same conditions, this product represented half of the total lysine content after four weeks of incubation at 37 degrees C. This adduct was isolated and identified as N epsilon-(carboxymethyl)lysine (CML) by TLC, GC/MS and amino acid analysis. Several oxidation products of ASA were each reacted with polylysine in the presence of sodium cyanoborohydride to identify the reactive species. CML was the major adduct formed with either ASA and dehydroascorbic acid (DHA). Markedly diminished amounts were seen with L-2,3-diketogulonic acid (DKG), and L-threose, while no CML was formed with L-threo-pentos-2-ulose (L-xylosone). In the absence of sodium cyanoborohydride the yield of CML was similar with each of the ASA autoxidation products and required oxygen. Reactions with [1-14C]ASA gave rise to [14C]CML, but only with NaCNBH3 present. At least two routes of CML formation appear to be operating depending upon whether NaCNBH3 is present to reduce the putative Schiff base formed between lysine and DHA.

Topics: 2,3-Diketogulonic Acid; Amino Acids; Animals; Ascorbic Acid; Borohydrides; Cattle; Crystallins; Kinetics; Lysine; Oxidation-Reduction; Polylysine

The oxidation of ascorbic acid leads to the formation of several compounds which are capable of reacting with protein amino groups via a Maillard reaction. Radioactivity from [1-14C]ascorbic acid was linearly incorporated into lens crystallins over a 10 day period in the presence of NaCNBH3. This rate of incorporation was 6-7-fold more rapid than that obtained with [14C]glucose under the same conditions. SDS-PAGE showed a linear incorporation into all the crystallin subunits. [1-14C]Ascorbic acid-label led alpha-crystallin was separated into its component A and B subunits, and each was digested with chymotrypsin. HPLC peptide analysis showed a differential labelling of the various lysine residues. Analysis of the peptides by mass spectrometry allowed the identification of the sites and the extent of modification. These values ranged from 6% for Lys-78 to 36% for Lys-11 in the A subunit and from 5% for Lys-82 to an average of 38% for the peptide containing Lys-166, Lys-174 and Lys-175 in the B subunit. Amino acid analysis demonstrated a single modification reaction producing N epsilon-(carboxymethyl)lysine. This agreed with the mass increase of 58 observed for each modified peptide.

Topics: Amino Acid Sequence; Amino Acids; Animals; Ascorbic Acid; Binding Sites; Borohydrides; Cattle; Chromatography, High Pressure Liquid; Chymotrypsin; Crystallins; Electrophoresis, Polyacrylamide Gel; Glucose; Glycosylation; Kinetics; Macromolecular Substances; Mass Spectrometry; Molecular Sequence Data; Pepsin A; Peptide Fragments

Incubation of neutral salt soluble type III pN-collagen with [14C]acetaldehyde in vitro resulted in the formation of spontaneously stable acetaldehyde-protein adducts. This reaction occurred primarily at lysine residues and it was not affected by 0.2-2 mM concentrations of ascorbate but addition of sodiumcyanoborohydride increased the stable adducts by 3-5-fold. When confluent cultures of human skin fibroblasts were incubated with physiologically relevant concentrations of acetaldehyde, it became covalently bound to type III procollagen secreted into the medium. We propose that acetaldehyde binding to collagen fibrils occurs in vivo following chronic alcohol consumption.

Topics: Acetaldehyde; Animals; Ascorbic Acid; Borohydrides; Cattle; Cells, Cultured; Collagen; Electrophoresis, Polyacrylamide Gel; Fibroblasts; Humans; Immunosorbent Techniques; Lysine; Macromolecular Substances; Serum Albumin, Bovine

The results of this study demonstrate that lysine is the major amino acid participating in the binding of acetaldehyde to proteins. The formation of both stable and unstable acetaldehyde-albumin adducts was shown to occur via the reaction of acetaldehyde with lysine residues. This conclusion was based on the following experimental evidence: (a) the ratio of stable to unstable adducts of bovine serum albumin was similar to that observed for polylysine; (b) acetylation of albumin markedly reduced acetaldehyde binding; (c) the radio-activity profiles (obtained by high-performance liquid chromatographic analysis) of [14C]acetaldehyde modified amino acids hydrolyzed from total and stable adducts of albumin were nearly identical to those of polylysine or alpha-t-boc-lysine. Analysis of stable adducts of albumin indicated two major modified lysine residues; one residue was much more acidic and the other more basic than unmodified lysine. Unstable adducts were shown to be Schiff bases since NaBH4 treatment resulted in the formation of N-ethyllysine residues. The reducing agents, NaCNBH3 and ascorbic acid, both increased stable adduct formation via increased binding to lysine residues; however, a different elution profile of modified lysine residues was observed for these reducing agents. NaCNBH3 increased the formation of N-ethyllysine residues exclusively, whereas ascorbate increased the formation of the acidic adduct of lysine and also caused the formation of an additional modified lysine residue which was present only in the ascorbate-treated polypeptides. In addition to their detection by radioactivity measurements, the acetaldehyde-lysine adducts could also be detected by the fluorescence of their ophthalaldehyde derivatives.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acetaldehyde; Animals; Ascorbic Acid; Borohydrides; Cattle; Chromatography, High Pressure Liquid; In Vitro Techniques; Lysine; Polylysine; Serum Albumin, Bovine