Intralumenal alkaline phosphatase of the calf intestine

About 80% of the total activity of the alkaline phosphatase of the calf intestine was found within the lumen and only 20% in the mucosa. The specific activity of the intralumenal enzyme fraction was about ten times higher than that of the mucosa enzyme. Differential centrifugation experiments demonstrated that the intralumenal enzyme of the proximal gut segment can be found in a fraction which exhibits sedimentation behaviour like a microsomal fraction, whilst the intralumenal enzyme of the distal gut segment was found to be soluble in the supernatant after centrifugation at 135000 X g for 60 min. Ouchterlony double diffusion analysis and antibody inhibition of alkaline phosphatase by antisera against the mucosa enzyme demonstrate that the two forms of intestinal enzyme have apparently identical antigenicity. Purified alkaline phosphatase obtained from the intralumenal fraction and from mucosa exhibits closely related pH-optima, Michaelis constants, amino acid inhibition type and inhibition constants. The results of large scale release of alkaline phosphatase bound to microvesicles are discussed with regard to results of morphological investigations in different tissues and cell cultures demonstrating the formation of intestinal membrane bodies and cell extrusion.