A kinetic study of rat salivary gland alkaline phosphatase and its inhibition by cadmium

Alkaline phosphatase, confined to myoepithelial cells and blood capillaries in rat submandibular salivary gland (SSG), may participate in the regulation of salivary flow. To determine whether the alkaline phosphatase of SSG has unique properties, comparative kinetic and inhibition studies on enzymes from SSG, intestine and kidney were performed. The K m values (at optimal pH for each tissue) of 0.34, 0.55 and 0.49 mM with p-nitrophenylphosphate for the enzymes from SSG, kidney and small intestine respectively were similar. However, in the presence of cadmium the K i values of 0.08 and 0.12 μM for the enzymes from SSG and kidney respectively were different from the value of 1.86μM for the enzyme from small intestine. Differences in K i values suggest differences in biochemical properties between the enzyme from small intestine and that isolated from SSG or kidney.