An optimized assay of alanine aminopeptidase activity in urine

Elaboration of an optimized kinetic test for urinary alanine aminopeptidase at 37 degrees C is described. As final concentrations, 50 mmol/L tris(hydroxymethyl)aminomethane x HCl buffer, pH 7.8, and 2 mmol/L alanine-4-nitroanilide are proposed. Five- to sixfold activitiy is obtained as compared with a generally used test procedure. Coefficients of variation for the method (within-run and between-day precision) ranged from 1.56 to 3.45%. Men excreted more alanine aminopeptidase than did women if urinary volume or urinary timed volume was used as basis of reference. We saw no sex-related differences in excretion of alanine aminopeptidase when enzyme excretion was related to urinary creatinine.