Membrane-bound and soluble polyphosphatases of mitochondria of Saccharomyces cerevisiae: identification and comparative characterization.

Isolated mitochondria of Saccharomyces cerevisiae possess polyphosphatases insensitive to a number of inhibitors of ATPase and pyrophosphatase of the same organelles and differing from the last two by neutral pH optima and molecular masses. After subfractionation of mitochondria, the polyphosphatase activity is distributed among the membrane and soluble preparations. The membrane-bound and soluble polyphosphatase activities are represented by different enzymes distinguished by molecular masses, substrate specificity, Km values, and relation to mono- and divalent cations. The membrane-bound polyphosphatases have molecular masses of 120 and 76 kDa, and the soluble one of about 36 kDa. All three enzymes appear to have a monomeric structure. The soluble polyphosphatase activity is stimulated by divalent cations in contrast to the membrane-bound one which is inhibited by the same cations, including Mg2+. Monovalent cations do not actually change the activity of the soluble enzyme, but stimulate it in the membrane preparation. Specific activities for the hydrolysis of polyphosphates with average chain lengths of 9-188 phosphate residues increase under increasing degree of substrate polymerization in the membrane preparation and are actually unchanged in the soluble one. The affinity of the soluble enzyme to polyphosphates is 5-10 times higher than that of the membrane-bound polyphosphatases.