Hydrolytic Proteins of Sugarcane: The Acid Phosphatases

Abstract

Acid phosphatases which readily hydrolyzed components of the adenylic acid system and phosphate monoesters were precipitated from cane-leaf extracts between 48- and 58-percent saturation with ammonium sulfate. The two general types were distinguished by their response to variable pH, substrate concentration, temperature, and inhibitors. ATP and ß-glycerophosphate were employed as representative substrates for the two groups. Both types of phosphatase were stimulated by arsenate. The ß-glycerophosphate reaction was inhibited by boron, zinc, manganese, bromide, copper, molybdenum, and tungsten. Molybdenum and tungsten also inhibited the ATP reaction. None of the inhibitors was effective in the presence of 10 µmoles per milliliter of arsenate. Copper appeared to serve as an activator in the presence of arsenate. Molybdenum and tungsten acted as competitive inhibitors of phosphatase. Molybdenum severely inhibited the ß-glycerophosphate reaction at 0.001 µmole per milliliter of digest, whereas 50 to 70 µmoles caused much of the activity to return. Both molybdenum and tungsten caused significant inhibition at concentrations as low as 0.0001 µmole per milliliter of digest. Tungsten was more effective than molybdenum against the ß-glycerophosphate reaction, causing significant suppression at concentrations 1/6 to 1/10 of the molybdenum levels needed for a comparable inhibition. Dialysis against distilled water had no appreciable effect on the phosphatase preparation. Meristem tissue was the best source of phosphatase, both in terms of specific activity and total phosphatase product. The possible mode of action of the inhibitor-activator relationships, and the significance of acid phosphatases in cane, is briefly discussed.