A hexose-1-phosphatase in silkworm blood

Abstract

Some of the properties of an enzyme present in silkworm blood which hydrolyzes glucose-1-phos-phate are described. Among a series of naturally occurring phosphate esters tested as substrates, only glucose-1-phosphate and galactose-1-phosphate are split. Synthetic p-nitrophenyl phosphate is hydrolyzed by the same enzyme. Enzyme activity is unaffected by addition of Mg ions to a non-dialyzed or dialyzed preparation, but is inhibited by fluoride, phosphate and arsenate. Fluoride is a competitive inhibitor of the enzyme. Optimum enzyme activity is at pH 4.0-4.5. Activity decreases sharply on the acid side, and more gradually on the alkaline side of the pH optimum. Silkworm blood preparation can be used to assay glucose-1-phosphate in mixtures with glucose-6-phosphate and ATP. The possibility is considered that the physiological role of the enzyme in silkworm is analogous to that of glucose-6-phosphatase in mammals.