In extracts from vegetative V12 the basal NAD-dependent glutamate dehydrogenase (NAD-GDH) activity was low, but it increased on standing at 4°C. When 0.1 mM-AMP was included in the assay mix, enzyme activity was stimulated nearly 30-fold. As the extract was allowed to age, the enzyme rapidly lost its ability to be stimulated by AMP. The response of NAD-GDH to AMP was also dependent on the stage of morphogenesis. The ratios of NAD-GDH activity assayed with and without AMP (+AMP/-AMP ratios) in freshly prepared extracts from cells at 0, 4, 8 and 12 h of development were similar, but declined later in morphogenesis. The + AMP/ - AMP ratio decreased sharply during activation at 4°C in extracts from cells at 0, 4, 16 and 20 h of development. By contrast, extracts from cells starved for 8 and 12 h remained more responsive to AMP throughout activation. Analysis of Western blots showed that vegetative NAD-GDH did not undergo any detectable proteolytic cleavage during 96 h of activation at 4°C. Also, no change in molecular mass appeared to take place within the cells until culmination (20–24 h), when some breakdown products appeared. Activation of NAD-GDH also occurred in strains NC4 and AX3, and in . In addition, the enzyme from these four strains was stimulated by AMP and the + AMP/ - AMP ratio declined with similar kinetics during activation. The enzyme from was not activated on standing, but it was stimulated by AMP. The effect of activation of NAD-GDH is discussed in relation to a postulated catabolic role for this enzyme.


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