Relation between Alkaline Phosphatase and Ca<Superscript>2+</Superscript>-ATPase in Calcium Transport

SEVERAL recent studies suggest that at least part of the effect of vitamin D on intestinal calcium transport may be mediated by a calcium-stimulated ATPase (Ca ATPase) situated in the brush borders of intestinal mucosal cells¹. Intestinal brush borders are known to contain several other enzymes which may be involved in digestion and transport, but the relationship between them is poorly understood². In the case of the disaccharidases, the question of the number of enzymes responsible for the various activities has been raised³. Alkaline phosphatase is also present in brush borders but its function is unknown. During studies of the effect of various agents On intestinal calcium transport we noted a close correlation between the activities of alkaline phosphatase and Ca ATPase. We therefore wondered whether the activities might be due to a single enzyme species. Haussler et al.⁴ and Norman et al.⁵ have also noted a close relationship between the two activities under a variety of conditions but Holdsworth⁶ thinks the two activities are not related. We report here further evidence, based on denaturation by heat and on various dietary manipulations in the rat, which suggest that the two enzymes may be part of a single enzyme complex.