92] Metaphosphatase

Abstract

The chapter describes the two distinct metaphosphatases: (1) an enzyme that produces orthophosphate from relatively low molecular weight substrates, (NaPO 3 ) 3 or (NaPO 3 ) 6 . It occurs in yeasts, molds, and various animal organs; (2) an enzyme, analogous to nucleic acid depolymerases, which depolymerizes metaphosphates of mol. wt. > 1,000,000 to smaller fragments without splitting off orthophosphate and occurs in some strains of Aspergillus and Penicillium and also in Proteus vulgaris . The production of orthophosphate from tri- or hexametaphosphate can be followed by measuring the reduction of phosphomolybdate at acid pH. In the course of procedure followed for low molecular weight substrates, the substrate can be made by melting of NaH 2 PO 4 and rapid cooling of the melt, or commercial tri- or hexametaphosphate preparations may be used if they are crystalline. In the course of procedure followed for high molecular weight substrates, The substrates are prepared by heating KH 2 PO 4 →(KPO 3 ) n , where n = 15,000 to 20,000. The breakdown of the high molecular weight substrates is followed by measuring the decrease in viscosity. In the course of purification procedure, animal tissue extracts or yeast plasmolyzates containing metaphosphatase are acetone-dried or precipitated with acetone, without further purification. Yeast metaphosphatase loses up to 40 % of its activity after incubating for 3 hours at 33°, but its activity is completely preserved in 50% glycerol solution, pH 7.