THE C-S LYSIS OF L-CYSTEINE CONJUGATES BY ASPARTATE AND ALANINE AMINOTRANSFERASE ENZYMES

One biotransformation pathway which is responsible for the generation of mutagenic and cytotoxic metabolites is that of the C-S lysis (CSL) of L-cysteine conjugates. Thirteen cysteine S-conjugates, synthesised in our laboratories, were incubated with porcine heart aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT), and the C-S lyase activity for each enzyme-substrate combination was determined. ASAT and ALAT were shown to exhibit CSL activity. It was also demonstrated that this activity was inhibited in the presence of the pyridoxal phosphate (PLP)-dependent enzyme inhibitor amino(oxyacetic acid) (AOAA) confirming the pyridoxal phosphate dependent mechanism by which C-S lysis is known to take place. Since the activities of these enzymes are used as biomarkers for the assessment of organ damage, the potential interaction of L-cysteine conjugates with them may suppress their activity through direct inhibition.