The effect of AMP on the NAD-dependent glutamate dehydrogenase during activation and morphogenesis in the cellular slime moulds

Abstract

In extracts from vegetative Dictyostelium discoideum V12 the basal NAD-dependent glutamate dehydrogenase (NAD-GDH) activity was low, but it increased on standing at 4 OC. 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 OC. Also, no change in molecular mass appeared to take place within the cells until culmination (2&24 h), when some breakdown products appeared. Activation of NAD-GDH also occurred in D. discoideum strains NC4 and AX3, and in D. mucoroides. 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 Polysphondylium violaceum 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.

Effect of the glutamine synthetase inhibitor, methionine sulfoximine, on the growth and differentiation of Dictyostelium discoideum

“…The simplest interpretation of these results is that other possible ammonia removing enzymes (e.g. NAD‐GDH) [18–20] are unable to lower the level of ammonia sufficiently for culmination to occur and it is only when GS activity reappears that this can happen.…”

Rapid patterning and zonal differentiation in a two-dimensionalDictyosteliumcell mass: the role of pH and ammonia

“…Similarly, differentiating cells show much faster patterning compared to freshly starved cells (S. Sawai, unpublished observation). This may also be due to the higher content of ammonia or higher activity of ammonia-regulating enzymes such as AMP-deaminase (Jahngen and Rossomando, 1986) and NAD-dependent glutamate dehydrogenase (Pamula and Wheldrake, 1992) in the cells at the later stages of development.…”