Die Aktivität von Phosphoglucose-Isomerase und Phosphoglucomutase während der Morphogenese kernhaltiger und kernloser Acetabularien

Summary

The activity of two enzymes of the UDP-glucose and UDP-galactose biosynthetic pathway—phosphoglucose-isomerase and phosphoglucomutase—have been followed during morphogenesis of the unicellular green alga Acetabularia mediterranea. We have found that the increase in enzyme activities during morphogenesis represents de novo synthesis. The kinetic constants (K _m, K _i) of phosphoglucose-isomerase are similar to those found for the enzyme from rabbit muscle; mannose-6-phosphate was found to be a competitive inhibitor.

The increase in activity of phosphoglucose-isomerase parallels the linear increase in total protein, neither showing changes with cap formation. In contrast, the activity of phosphoglucomutase is enhanced markedly when cap formation starts.

Whether the nucleus is present or absent does not affect the above mentioned properties of the two enzymes. From this fact we conclude that the enzyme syntheses are regulated by the cytoplasm, probably at the level of translation. Contributions of DNA from chloroplasts and mitochondria can be excluded because in anucleate cells, which have an already established gradient of m-RNA, actinomycin D (10 μg/ml) has no effect on the synthesis of these enzymes.

There are also differences in the spatial distribution of the two enzymes. We were able to show that both enzymes are synthesized unequally in different regions of the cells.