Purification of an alkaline phosphatase-lipoprotein-X complex.

Abstract

An alkaline phosphatase isoenzyme was observed in an abnormal position in the agar-agarose gel pattern of sera from several patients suffering from intrahepatic and extrahepatic cholestasis. We purified this isoenzyme, by gel filtration and affinity chromatography, from the serum of a patient suffering from extrahepatic cholestasis. Analysis demonstrated an alkaline phosphatase-lipoprotein-X complex with a relative molecular mass of at least 669,000. We discuss the interpretation of alkaline phosphatase isoenzyme patterns produced by different techniques.

Liver Plasma Membrane: the Source of High Molecular Weight Alkaline Phosphatase in Human Serum

“…The specific antiserum obtained against the high molecular weight multienzyme complex did not react by immunofluorescence with serum lipoproteins nor with lipoprotein X. This argues in favor of at least part of the high molecular weight structure in cholestatic serum not being lipoprotein X carrying ALP, in contrast to what was proposed by others (50)(51)(52).…”

“…DE BROE ET AL. HEPATOLOGY low densities in sucrose (49,50) and in other media, most likely corresponds to P-lipoprotein or lipoprotein X enzyme complexes (48, 51,52). Electron microscopy of the isolated high molecular weight material with direct methods and after preparation by thin-sectioning techniques reveals vesicles with a triple-layered membrane with ALP activity on the outside or the inside of that membrane.…”

“…An increased amount of solubilized unbound enzymes or enzymes bound to plasma membrane fragments (high molecular weight) may reach the serum and bile. It is probable that solubilized plasma membrane enzymes reaggregate with lipids and lipoproteins in serum (50)(51)(52), resulting in a second population of high molecular weight structures in which enzymes are detected.…”