DETECTION AND SOME PROPERTIES OF MEMBRANE-BOUND AND SOLUBLE POLYPHOSPHATASES IN MITOCHONDRIA OF THE YEAST SACCHAROMYCES-CEREVISIAE

Saccharomyces cerevisiae mitochondria possess polyphosphatases that ar e tightly bound to the membranes and differ from soluble polyphosphata se of these organelles in a number of properties. Molecular weights of the membrane-bound polyphosphatases are 120 and 76 kD, and the molecu lar weight of the soluble polyphosphatase is about 36 kD. All three en zymes are evidently monomers, since antibodies against purified cell-e nvelope polyphosphatase of S, cerevisiae reacted with 115, 78, and 37 kD polypeptides in immunoblotting. The activities of membrane-bound an d soluble polyphosphatase are maximal at neutral pH. The soluble polyp hosphatase activity is stimulated by divalent cations, unlike the memb rane-bound enzymes which are inhibited by the same cations including M g2+. Monovalent cations do not affect the activity of the soluble enzy me but stimulate polyphosphatases in the membrane preparation. The spe cific activities for hydrolysis of polyphosphates with average chain l engths of 9 to 188 phosphate residues are enhanced by increasing the d egree of substrate polymerization in the case of the membrane preparat ion and are unchanged in case of the soluble enzyme, Affinity of the s oluble enzyme to polyphosphates is 5-10 times higher than that of the membrane-bound polyphosphatases. In the soluble fraction of mitochondr ia, high tripolyphosphatase activity is detected which is similar to 8 0% of that in isolated mitochondria.