SALINITY-SENSITIVE ALKALINE-PHOSPHATASE ACTIVITY IN GILLS OF THE BLUE-CRAB, CALLINECTES-SAPIDUS RATHBUN

A levamisole-sensitive (K-i = 0.72 mM) alkaline phosphatase (pH optimu m 9.1) and a levamisole-insensitive alkaline phosphatase (pH optimum 7 .1) are present in gills of the blue crab Callinectes sapidus. Both en zymes are distinct from ouabain-sensitive ATPase. Specific activity fo r either phosphatase is greatest in the acinar tissue, which lines the branchial vessels. Histochemical localization of the enzymes confirme d this distribution. Activity of levamisole-sensitive alkaline phospha tase is affected by acclimation salinity. V-max of the levamisole-sens itive alkaline phosphatase is greater in high-salinity crabs than in l ow-salinity crabs; apparent K-m is not significantly different. The Le vamisole-sensitive alkaline phosphatase associated with the acinar tis sue lining the branchial vessels may modulate the osmoregulatory respo nse in blue crabs.