Abstract
1. Four fractions of kidney alkaline phosphatase were prepared by chromatography on DEAE-Sephadex. An investigation of their properties suggests that the fractions represent modifications of a single kidney enzyme. 2. Urinary alkaline phosphatase resembles kidney enzyme in most of its properties, but differs in Km and in the degree by which it is activated by Mg2+ ions. 3. Estimates of the molecular weights of kidney and urinary alkaline phosphatase gave values of 150000–170000 for kidney phosphatase and 75000 for the urinary enzyme. 4. It is suggested that urinary alkaline phosphatase is a sub-unit of kidney phosphatase, but it has not been possible to simulate the formation of urinary enzyme by treating kidney enzyme with urea or H+ ions.