ALKALINE-PHOSPHATASE FROM ATLANTIC COD (GADUS-MORHUA) - KINETIC AND STRUCTURAL-PROPERTIES WHICH INDICATE ADAPTATION TO LOW-TEMPERATURES

Alkaline phosphatase was purified from the pyloric caeca of Atlantic c od in a procedure requiring column chromatography on phenyl-Sepharose, Q-Sepharose, Sephacryl S-300, Reactive Red and concanavalin-A-Sepharo se. The enzyme is a dimeric glycoprotein of identical 70 kDa subunits and partly associated with membranes, It was inactivated by EDTA and c ould be reactivated with zinc and magnesium, The catalytic efficiency (k(cat)/K-m) of the cod enzyme was found to be 2.5-fold greater in com parison with the calf intestinal enzyme, The cod enzyme was unstable t owards heating above 40 degrees C whereas the calf enzyme remained sta ble at temperatures up to 55 degrees C. Differences were also found in the response to some commonly used inhibitors, where the cod intestin al alkaline phosphatase resembled most the liver/bone/kidney isozyme f rom humans, Notably, the sensitivity towards phosphate inhibition was lower with the cod enzyme, and the pH optimum for catalysis was differ ent, We conclude that the observed kinetic differences are indicative of cold-adaptation. Fewer stabilizing interactions in the cod enzyme s tructure, as evidenced by lower thermal stability, would help to maint ain necessary flexibility at the low level of thermal energy in the bo dy of this ectothermic species.