Intestinal alkaline phosphatase in bile: evidence for an enterohepatic circulation.

The isoenzyme characteristics of alkaline phosphatase in human bile obtained from patients with gallstones have been determined by means of electrophoresis on polyacrylamide gel, both before and after preincubation with neuraminidase, and also by means of inhibition tests with heat, urea, and L-phenylalanine. Bile alkaline phosphatase is shown to be partly secreted by the liver cell, but partly derived from the small intestine. The presence of small-intestinal alkaline phosphatase in bile implies an enterohepatic circulation of this high molecular weight glycoprotein. The significance of this finding is discussed in relation to the mechanism whereby large protein molecules may pass across the plasma membrane of the liver cell.