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In experimental bile obstruction the serum activities of the membrane-bound liver enzymes, alkaline phosphatase, 5'-nucleotidase and γ-glutamyltransferase are greatly increased, whereas in the liver only the alkaline phosphatase activity is elevated. After partial hepatectomy or tetrachloride poisoning the alkaline phosphatase activity in the regenerating liver is increased to the same extent as in cholestasis without an accompanying elevation in serum activity. The following results support the hypothesis of a bile salt-mediated solubilization of membrane-bound enzymes in cholestatic liver: (1) 30 min after bile duct ligation the total bile acids in the liver were increased 5-fold, 2 h later as much as 10-fold. After 1 day, the bile acid concentration was still 4 times above normal. (2) Isolated plasma membranes from normal and obstructed livers were incubated in vitro with increasing amounts of tri- and dihydroxycholanic acids. At a final concentration of 1 mmol/1 taurochenodeoxycholate significant amounts of membrane-bound enzymes were released into the 12,000-g supernatant. (3) In the regenerating liver, where tissue phosphatase activity was high and serum phosphatase activity unchanged, the bile salt concentration was not increased.

Alkaline phosphatase (EC 3.1.3.1) activity increases 5-15 fold in the livers of rats, following bile duct ligation. The mechanism of this increase has been the subject of numerous investigations. In HeLa cells the synthesis of a different phosphatase enzyme protein with higher catalytic activity has been postulated.After preparing an antiserum against rat liver phosphatase, we compared the phosphatase protein concentration in normal and cholestatic livers by immunochemical titration. Our results clearly indicate that the elevation of enzyme activity is due to an increased accumulation of enzyme protein. Der Mechanismus des Aktivitätsanstiegs der alkalischen Leber phosphatase bei experimenteller Cholestase: Messung einer erhöhten Enzymkonzentration durch Immuntitration

Es wird die Umsetzung von 4-Nitrophenylphosphat durch cholestatisches Ratten-und Humanserum in Diäthanolaminpuffer unterschiedlicher Konzentration bei verschiedenen pH-Werten untersucht. Es konnte eine Phosphorylierung des Diäthanolamin durch 4-Nitrophenylphosphat und Alkalische Phosphatase nachgewiesen werden. The pbosphorylation of diethanolamine by alkaline phosphataseThe action of cholestatic serum of man and rat on 4-nitrophenylphosphate and diethanolamine was studied at different pH values in different concentrations of diethanolamine buffer. A phosphorylation of diethanolamine by 4-nitrophenylphosphate und alkaline phosphatase was shown.

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