Behaviour of urinary dipeptidase in patients with chronic renal failure

Renal dipeptidase (EC 3.4.13.19) activity in serum and urine from healthy volunteers (n = 20), patients with diabetes (n = 18) and patients with chronic renal failure (n = 5) was measured using glycyl-D-alanine as substrate. The assay was highly specific for the enzyme and was not affected by the various aminopeptidases present in serum and urine. No difference in serum renal dipeptidase activity was observed between the groups. The enzyme activity (U/L) in urine was higher than that in serum, irrespective of the group, suggesting the urine concentration was not affected by the serum concentration. The mean renal dipeptidase activities in urine were 2.56, 2.46 and 0.78 U/mol creatinine for healthy subjects, patients with diabetes and patients with chronic renal failure, respectively. The renal dipeptidase activity was significantly lower in the chronic renal failure group. The urinary excretion of dipeptidase (U/mmol creatinine) showed significant inverse correlations with that of beta 2-microglobulin, albumin and alpha 1-microglobulin, and with serum concentrations of creatinine, beta 2-microglobulin and alpha 1-microglobulin. We suggest that urine dipeptidase may be a useful marker of renal diseases.