Genetic and biochemical studies of the hexose monophosphate shunt in <i>Neurospora crassa</i>. II. Characterization of biochemical defects of the morphological mutants colonial 2 and colonial 3

Abstract

The two dehydrogenases of the hexose monophosphate shunt, glucose-6-phosphate dehydrogenase and 6-phosphogluconic acid dehydrogenase, were examined in two morphology mutants of Neurospora crassa. Glucose-6-phosphate dehydrogenase extracted from the mutant colonial-2 was found in an altered form as compared to the wild-type enzyme. The second enzyme of the pathway was observed to be abnormal in the mutant colonial-3. In addition, 6-phosphogluconic acid dehydrogenase was found to exhibit non-classical kinetics. The data indicate that the altered morphology exhibited by both colonial-2 and colonial-3 is due to the suboptimal capacity of the hexose monophosphate shunt to function normally. This physiological impairment of the pathway is reflected in a lowered cellular steady-state level of NADP.