Generation of acetate and production of ethyl-lysine in the reaction of acetaldehyde plus serum albumin

We report that incubation of acetaldehyde with bovine serum albumin results in the generation of acetate in a reaction that is directly proportional t o the levels of albumin and exponentially dependent on the concentration of acetaldehyde. Both reactants need to be present for acetate to be formed. The oxidation of acetaldehyde into acetate requires that a reduced product also be generated in the reaction. It was hypothesized that, at high concen trations, acetaldehyde itself may reduce the Schiff bases formed in the rea ction of a second molecule of acetaldehyde with amino groups in the protein , resulting in the generation of ethyl-lysine moieties. Incubation of aceta ldehyde (240 mM) with bovine serum albumin was found to generate ethyl-lysi ne moieties as determined by a specific monoclonal antibody. Immunization o f rabbits with products of the reaction of bovine serum albumin with acetal dehyde led to the generation of antibodies that reacted to reduced adducts formed in the reaction of acetaldehyde and proteins in the presence of sodi um cyanoborohydride. However, the generation of acetate from acetaldehyde p lus albumin was 60-fold greater than could be explained by the reduction of Schiff bases, as determined by the maximal incorporation of [C-14]-acetald ehyde into an acid-precipitable protein fraction. Thus, other mechanisms to generate acetate also occur. The present findings provide an explanation f or earlier reports that acetaldehyde adducts formed under "nonreducing" con ditions generate antibodies that recognize reduced acetaldehyde protein add ucts. However, the mechanism by which the bulk of acetate is generated in t he reaction of acetaldehyde and bovine serum albumin remains to be elucidat ed. (C) 1998 Elsevier Science Inc.