ELIMINATION OF ALKALINE-PHOSPHATASES FROM CIRCULATION BY THE GALACTOSE RECEPTOR - DIFFERENT ISOFORMS ARE CLEARED AT VARIOUS RATES

Three isoforms of human alkaline phosphatase (liver, bone and placenta l ALP) were purified and their elimination studied after intravenous i njection in rats. The rates of elimination were significantly inhibite d by prior injection of asialofetuin, indicating that the uptake was m ediated by the galactose receptor in liver. Their relative clearance r ates differed, being rapid for the bone ALP, significantly slower for the liver isoform and very slow for the placental ALP. The bone ALP sh owed a rapid initial clearance, apparently related to its large glycan heterogeneity and to the presence of molecules with a low sialic acid content. When isolated from serum the liver and bone ALP isoforms sho wed clearance rates differing slightly from those of the organ derived forms. We conclude that differences in carbohydrate structure and amo unt of sialic acid of the three isoforms result in various clearance r ates. These differences will also affect their serum concentrations as well as the composition and heterogeneity of the individual isoforms in serum. (C) 1998 Elsevier Science B.V.