Urinary aspartate transaminase (AST) activity and detection of its inhibitors in normal urine.

Urinary aspartate-transaminase activity in the whole urine was found to be mean +/- S.D. = 8.46 +/- 0.69 l.U/l when measured immediately after urine collection. About 50% loss in enzyme activity was observed after 18 hours dialysis. An overall 176% increase in enzyme activity followed by Sephadex G-25 (fine) whole urine fractionation and a highly significant (P less than .001) partial inhibition by earlier Sephadex fractions and maximum inhibition by earlier Sephadex fractions and maximum inhibition of enzyme by fraction 7 have suggested the presence of both high and low molecular weight urinary inhibitors of aspartate-transaminase. Urea and ammonia presence and inhibitor activity in fraction 6 to 8 bear a close parallelism; both the substances produced 31% inhibition of partially purified goat liver GOT at concentrations approximating normal human urine. Therefore, low enzyme activity and its substantial loss in the whole urine and during dialysis may be due to the concomitant inhibitory effects of urea, ammonia and unidentified nature of high molecular weight substance(s). The present method may be effective in separating inhibitors and overcoming the disadvantages of dialysis in determining true urinary aspartate-transaminase activity.