An acid phosphatase EC 3.1.3.2 ofT. thiooxidanscells hydrolyzed pNPP most rapidly at pH 2.5. The addition of sulfate ions to the reaction mixture markedly stimulated the enzyme activity and shifted the pH optimum to the neutral side with increasing concentration of sulfate.The enzyme was solubilized and purified 360-fold with a 6recovery. It was significantly activated by sulfate ions, with an optimum pH of 4.5 at maximum activation. The substrate specificity was found to be fairly broad and a-glycerophosphate was cleaved most rapidly among many phosphate esters tested. It was inhibited by fluoride, molybdate, inorganic phosphate, arsenate, and ascorbate. The molecular weight was estimated to be 130,000 by the gel filtration method.
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