L-homoarginine, a specific inhibitor of liver-type alkaline phosphatase, applied to the recognition of liver-type enzyme activity in rat intestine.

Abstract

l-Homoarginine, an inhibitor of alkaline phosphatase, has been applied for the study of the localization of alkaline phosphatase activity in rat liver and intestine. Five substrates were employed: Na α-naphthyl acid phosphate, naphthol AS-BI phosphate, Na β-glycerophosphate, o-carboxyphenylphosphate and O-ethanolamine phosphate. Diazonium coupling was employed with the naphthol substrates; the Gomori calcium-cobalt method was used with the others. Each substrate was also employed in the presence of 12.5 mMl-phenylalanine, an intestinal (brush border-specific) alkaline phosphatase inhibitor. The liver-type enzyme, in both the liver parenchyma and the lamina propria of the small intestine, was sensitive to 12.5 mMl-homoarginine in varying degrees, depending on the substrate used. With Na α-naphthyl acid phosphate, a total inhibition was observed histochemically; l-homoarginine inhibited partially purified liver alkaline phosphatase by 97%, as measured biochemically. The alkaline phosphatase of leukocytes and macrophages of the intestinal lamina propria was inhibited in the presence of l-homoarginine but not of l-phenylalanine. Reactive elements that resembled the macrophages of the lamina propria were present in the liver. The activity in these cells was also inhibited by l-homoarginine.