カツオ肝蔵のNAD(P)加水分解酵素-3-nucleotide pyrophosphataseの単離精製とその諸性質〔英文〕

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Nucleotide pyrophosphatase was purified from skipjack liver by various types of column chromatography and gel filtration. The enzyme was ultimately purified aout 2, 900-fold. It was homogeneous in polyacrylamide gel electrophoresis, but exhibited a slight alkaline phosphatase activity, sugesting same persistent contamination. It was found by analytical gel filtration and SDS gel electrophoresis that the enzyme has a molecular weight of 86, 000 and is composed of a single polypeptide chain. The isoelectric point was determined to be 4.8 by isoelectrofocusing.The enzyme showed its maximum activity at around pH9 when NAD or 2'-deoxythymidine-5'-p-nitrophenyl phosphate was used as the substrate. It was to some extent activated by Mg2+, but inhibited by other metal ions, such as Mn2+, Fe2+, Fe3+, Ca2+, as well as by several chelating agents. The enzyme was inhibited competitively by 5'-AMP and nicotinamide mononucleotide, both of which are reaction products from NAD, and also by other nucleotides. The skipjack enzyme showed a higher affinity and maximum velocity for NADH2 than for NAD (P). The enzyme hydrolyzed various sugar nucleotides, ATP, ADP, and inorganic pyrophosphate, thus indicating a low substrate specificity.
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