Title: Similarity between alkaline phosphatase and nucleotide pyrophosphatase from skipjack liver.
Abstract: Skipjack liver alkaline phosphatase (EC 3.1.3.1) and nucleotide pyrophosphatase (EC 3.6.1.9) were compared in respect to some physico-chemical and enzymatic properties. Neuraminidase storgly inactivated both enzymes in a similar fashion, whereas muramidase inactivated alkaline phosphatase more slowly than the other enzyme. Nucleotide pyrophosphatase was also inactivated by several proteolytic enzymes more easily than alkaline phosphatase. Sodium lauryl sulfate, urea, and guanidine hydrochloride inactivated both enzymes in a similar manner, and the protective effect of MgCl2 was also similar. In the presence of MgCl2, alkaline phosphatase showed the optimum temperature at 35°C and nucleotide pyrophosphatase at 45°C. In the absence of MgCl2, however, both enzymes showed the identical optimal temperature at 45°C. All the substrates common to both enzymes inhibited them competitively. Nucleotide pyrophosphatase was inhibited by all the substrates specific to alkaline phosphatase but the inhibition types were different for both enzymes with some substrates. All the substrates for nucleotide pyrophosphatase also inhibited alkaline phosphatase by the competitive or the mixed type manner. These results suggested that the two skipjack enzymes are closely similar to each other in their primary or higherdimentional structure.