Neutral arylamidase in urine of healthy and nephrotic children.

The neutral arylamidase activity in urine of healthy and nephrotic children was determined using L-leucyl-beta-napthylamide as substrate. The neutral arylamidase activity in urine samples from 13 nephrotic children (22.4+/-3.0 (S.E.) mumol/min/g of creatinine) was significantly higher (p less than 0.001) than that from 27 normal children (8.5+/-0.4). Two forms of neutral arylamidase were demonstrated by polyacrylamide gel electrophoresis and Sephadex G-200 gel filtration in urine samples from normal children. One was a high molecular weight arylamidase (more than 1 000 000), the other had a molecular weitht of 240 000 as estimated by Sephadex G-200 gel filtration. Two additional electrophoretically distinct froms of neurtral arylamidase were demonstrated on polyacrylamide gel in urine samples from nephrotic children. Two neutral arylamidases from normal children, one additional arylamidase from normal children, one additional arylamidase from nephrotic children and kidney membrane-bound neurtral arylamidase had identical KM values, effect of inhibition by L-methionine and heat stability. One of four urinary arylamidases from nephrotic children was suggested to be derived from plasma. It is concluded that an increase in urinary neutral arylamidase activity in nephrotic children is not only due to increased released from kidney membranes, but also due to leakage of plasma neutral arylamidase in the urine.