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

To examine further the role of the enzyme glutamine synthetase in Dictyostelium discoideum we report here the effects of a specific glutamine synthetase inhibitor, methionine sulfoximine, on the growth and differentiation of this organism. Vegetative AX3 cells grown in the presence of methionine sulfoximine did not complete culmination in the normal time but were blocked at the finger stage. In these cells glutamine synthetase activity was almost completely abolished. However, methionine sulfoximine did not affect the level of glutamine synthetase mRNA, suggesting that there is no link between glutamine synthetase activity and mRNA transcription. Eventually glutamine synthetase activity reappeared and at the time culmination occurred. These results suggest that glutamine synthetase plays an important role in the assimilation of ammonia during the later stages of development in D. discoideum and that this assimilation is necessary for the completion of culmination.