AN ECTO-ENZYME FROM SULFOLOBUS-ACIDOCALDARIUS STRAIN-7 WHICH CATALYZES HYDROLYSIS OF INORGANIC PYROPHOSPHATE, ATP, AND ADP - PURIFICATION AND CHARACTERIZATION

Membranes of Sulfolobus acidocaldarius, a thermoacidophilic archaebacterium, show novel enzymatic activities to hydrolyze PP(i), ATP, and ADP at an optimal pH of 3, equal to the growth optimum. The activity increased by about 2-fold on addition of PP(i) and/or P(i) to the growth medium, when yeast extract and casamino acids were removed. The enzyme which hydrolyzes PP(i) at pH 3 was solubilized and purified by successive chromatographies. The final preparation showed a 26 kDa single band on SDS-PAGE, and a molecular mass of 35 kDa on gel permeation chromatography. The K(m) and V(max) for PP(i) were 0.16 mM and 33 mumol P(i) released/min/mg at 55-degrees-C. ATP and ADP were also good substrates. Divalent cations were not essential for activity. Substrate inhibition at more than 5 mM PP(i), ATP or ADP was observed. AMP, glucose-6-phosphate, and p-nitrophenyl phosphate were not hydrolyzed at all. The activity was 4-fold stimulated by addition of the lipid fraction extracted from the organism.