1-Methyladenosine Hydrolase of Starfish (Pisaster ochraceous)

Abstract

A nucleosidase specific for 1-methyladenosine was purified up to 42-fold from mature testes of starfish, and less extensively from mature ovaries, stomach tissue, and pyloric caeca, by extraction, ammonium sulphate fractionation, and DEAE-cellulose chromatography. The enzyme, the products of which were 1-methyladenine and D-ribose, was free from nucleoside phosphorylase activity and had the following properties. The pH optimum was 7.8–8.0 with half maximum activity at pH 6.2 and 9.5; the enzyme was rapidly inactivated at 40 C and by freezing and thawing; of 10 purine and pyrimidine ribonucleosides and deoxyribonucleosides studied, only 1-methyladenosine was hydrolyzed; the Km was 6.65–7.15 × 10−4 M; 1-methylinosine and 1-methylguanosine were noncompetitive inhibitors; the Ki for these were 1.25 × 10−4 M and 1.4 × 10−4 M, respectively. Vmax values of from 6.3–10.4 μmoles of 1-methyladenosine hydrolyzed per mg of enzyme protein per hr at 25 C were calculated. It is not known if this enzyme plays a role in the in vivo formation of 1-methyladenine, which induces maturation of starfish oocytes.