Diuresis-dependent excretion of multiple forms of renal brush-border enzymes in urine

The urinary brush-border enzymes alanine aminopeptidase (EC 3.4.11.2), alkaline phosphatase (EC 3.1.3.1) and gamma-glutamyltransferase (EC 2.3.2.2) and their activity pattern of soluble and particulate forms separated by ultracentrifugation were investigated over 8 h after a high intake of fluid (22 ml/kg body wt.). The activity pattern of the two multiple forms was markedly influenced by the urine flow rate. The time-related excretion of soluble forms of these three enzymes increased with the extent of urine output whereas the excretion of particulate form was independent on diuresis. Diuresis-dependent excretion of total activities of brush-border enzymes can be exclusively considered to be a consequence of changed excretion of soluble forms.