Detection and some properties of membrane-bound and soluble polyphosphatases in mitochondria of the yeast Saccharomyces cerevisiae

Saccharomyces cerevisiae mitochondria possess polyphosphatases that are tightly bound to the membranes and differ from soluble polyphosphatase of these organelles in a number of properties. Molecular weights of the membrane-bound polyphosphatases are 120 and 76 kD, and the molecular weight of the soluble polyphosphatase is about 36 kD. All three enzymes are evidently monomers, since antibodies against purified cell-envelope polyphosphatase of S. cerevisiae reacted with 115, 78, and 37 kD polypeptides in immunoblotting. The activities of membrane-bound and soluble polyphosphatase are maximal at neutral pH. The soluble polyphosphatase activity is stimulated by divalent cations, unlike the membrane-bound enzymes which are inhibited by the same cations including Mg2+. Monovalent cations do not affect the activity of the soluble enzyme but stimulate polyphosphatases in the membrane preparation. The specific activities for hydrolysis of polyphosphates with average chain lengths of 9 to 188 phosphate residues are enhanced by increasing the degree of substrate polymerization in the case of the membrane preparation and are unchanged in case of the soluble enzyme. Affinity of the soluble enzyme to polyphosphates is 5-10 times higher than that of the membrane-bound polyphosphatases. In the soluble fraction of mitochondria, high tripolyphosphatase activity is detected which is approximately 80% of that in isolated mitochondria.