De novo synthesis of glucose-6-phosphate- (E.C. 1.1.1.49) and 6-phosphogluconate dehydrogenase (E.C. 1.1.1.44) in plant storage tissue slices.

Resting potato tuber tissue possesses only faint activity of the two dehydrogenases of the oxi­ dative pentose phosphate cycle, glucose-6-phosphateand 6-phosphogluconate dehydrogenase. Slicing of the tissue, however, greatly enhances the action of both enzymes. The slicing-induced increase in activity is a consequence of intensified action of at least 5 glucose-6-phosphate dehydrogenase isozymes and a more differentiated activation/inactivation of seven 6-phosphogluconate dehydro­ genase isozymes. Using density labelling and isopycnic equilibrium centrifugation it could be demonstrated, that the bulk of both enzymes appearing after slicing the tissue is the result of de novo synthesis rather than activation of pre-existing proenzymes.