The hydrolysis of glucose monophosphates by a phosphatase preparation from pea seeds.

Although many phosphatase preparations have been obtained from plant tissues there are few data available on the breakdown of glucose monophosphates, and of glucose 1-phosphate in particular. In the work of Porter (1953), Spencer (1954) and Roberts (1956), it was found that glucose 1phosphate was hydrolysed by extracts from potato tubers, tomato leaves and wheat leaves respectively; however, more information is desirable on whether glucose 1-phosphate was hydrolysed directly, or through the intermediate formation of glucose 6-phosphate by phosphoglucomutase and the subsequent hydrolysis of the 6-ester. Axelrod (1947) found that glucose 1-phosphate was not hydrolysed by the acid phosphatase of citrus fruit although other phosphoric compounds such as fructose 1:6-diphosphate were hydrolysed. With extracts from some animal tissues it has been shown that the hydrolysis of glucose 1phosphate may take place via glucose 6-phosphate. Broh-Kahn & Mirsky (1948) could find no evidence for the existence of a glucose -phosphatase in liver extracts, and Goodlad & Mills (1957) concluded that the main route of glucose 1-phosphate hydrolysis in rat liver is through a preliminary conversion into glucose 6-phosphate. The direct hydrolysis of glucose 1-phosphate by a hexose 1-phosphatase from silkworm blood was reported by Faulkner (1955); this extract did not attack glucose 6phosphate. Morton (1955) found that purified alkaline phosphatases from cow's milk and calf intestinal mucosa hydrolysed both glucose 1phosphate and glucose 6-phosphate. Previous investigations (Turner & Turner, 1957) had indicated the presence of glucose monophosphatase activity in extracts from pea seeds. When glucose 1-phosphate was incubated with these extracts, glucose and inorganic phosphate were formed. However, further work was needed to establish that this hydrolysis did not proceed by way of glucose 6-phosphate. In the present investigation the acid phosphatase from pea seeds was purified 20-fold and a number of its properties studied. Both glucose 1-phosphate and glucose 6-phosphate were hydrolysed directly although the rate of hydrolysis of glucose 6-phosphate was higher than that of glucose 1-phosphate. Inorganic phosphate acted as a competitive inhibitor of the phosphatase action.