Aspects of regulation in kidney at the enzymic level: aldolase isozymes, aminopeptidase and alkaline phosphatase.

Histochemical and immuno-histochemical studies on kidney sections of adult rats and rats at different stages of development were carried out to estimate enzyme concentrations in nephron segments. Aminopeptidase and alkaline phosphatase were found from 3 days before birth in proximal tubule cells, aldolase-B and aldolase-A in all the nephron and collecting duct. The concentration of the enzymes remained remarkably constant from the 3rd day after birth onwards, except for aldolase-A in the distal tubule cells. The concentration of aldolase-B was higher than of aldolase-A in the distal tubule cells. The concentration of aldolase-B was higher than of aldolase-A, in glomerula and proximal tubules, that of aldolase-A was higher than that of aldolase-B in the ascending thick part of the Henle loop and in the following parts of the nephron. This implies that the concentration of the enzymes is the limiting factor for the regulation of substrate hydrolysis and that the nephron when formed can function as efficiently as the nephron of the adult rat with respect to these enzymes.