PRODUCTION AND UTILIZATION OF GLUCOSE 1-PHOSPHATE IN THE EGGS OF THE SEA URCHIN ANTHOCIDARIS CRASSISPINA

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Abstract
Concentrations of G1P, G6P, UDPG [uridine diphosphate glucose], UTP [uridine triphosphate] and PPi were measured in the eggs of the sea urchin, A. crassispina. Activities of phosphorylase a (EC 2.4.1.1), phosphoglucomutase (EC 2.7.5.1), UDPG pyrophosphorylase (EC 2.7.7.9) and pyrophosphatase (EC 3.6.1.1) were estimated. Levels of G1P and G6P increase following fertilization, but concentrations of UDPG and UTP in unfertilized eggs are similar to those in fertilized eggs. PPi is undetectable. In unfertilized and fertilized eggs, G1P level is very low compared with G6P level, and is far less than that expected from the equilibrium constant in a reaction catalyzed by phosphoglucomutase. Since phosphoglucomutase activity is higher by about 20 times than the phosphorylase a activity, G1P is probably produced in the reverse reaction, catalyzed by phosphoglucomutase, rather than in the reaction catalyzed by phosphorylase. The G1P produced seems to be utilized thoroughly in the reaction catalyzed by UDPG pyrophosphorylase. The reaction seems irreversible and tends to go to UDPG production in sea urchin eggs, since the PPi level is negligible due to high pyrophosphatase activity. The utilization of G1P in the reaction catalyzed by UDPG pyrophosphorylase seems to keep the G1P level low.