Studies on casein. 2. The action of phosphatases on caseins and low-molecular-weight phosphates

Abstract

The action of purified phosphoprotein phosphatase and prostate phosphomonoesterase on various caseins and on a number of low-molecular-weight phosphates was studied. The phosphoprotein phosphatase preparation showed highest activity towards substrates which had a phosphate group esterified with aromatic hydroxyl groups, towards [alpha]- and [beta]-caseins from cow''s and goat''s milk, inorganic pyrophosphate and acetyl phosphate; ribonucleotides and phosphoamides were hydrolyzed to a smaller extent. Little or no activity was shown by the enzyme towards phosphodiesters, O-serine phosphate, O-threonine phosphate, [alpha]- and [beta]-glycerol phosphate and disubstituted pyrophosphate. Prostate phosphatase, with a very high activity towards [beta]-glycerol phosphate and phenyl phosphate, liberated inorganic P only very slowly from a-caseins and goat''s [beta]-casein, and not at all from cows [beta]-casein. The results are discussed in relation to the nature of the phosphorus linkages in caseins.