Disappearance rates of intravenously injected canine alkaline phosphatase isoenzymes

The serum half-life of various canine alkaline phosphatase isoenzymes has been determined. Isoenzymes can be divided into 2 groups with regard to their half-life. Isoenzymes with a half-life of approximately 3 days include the hepatic alkaline phosphatase and the steroid-induced alkaline phosphatase. Those with a half-life of under 6 minutes include the alkaline phosphatase from placenta, kidney, intestine, and the hepatic and steroid-induced iosenzymes after removal of sialic acid. The inability to demonstrate some of the isoenzymes of alkaline phosphatase in serum of diseases animals is attributed to their short half-life. The relationship of the short half-life to the sialic acid moiety of the protein is discussed.