Ammonia Regulation of Intermediary Metabolism in Photosynthesizing and Respiring Chlorella pyrenoidosa : Comparative Effects of Methylamine

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Methylamine added to the medium of the unicellular alga Chlorella pyrenoidosa causes most of the shifts in carbon metabolism previously observed with ammonia addition. The most prominent and reproducible effect seen is a greatly increased flow of carbon from triose phosphates into alanine, aspartate, and glutamate, and acids of the tricarboxylic acid cycle including malate, fumarate, and citrate. The large increase in synthesis of glutamine seen with ammonia addition does not occur with methylamine addition. It is concluded that accelerated glutamine synthesis per se is not the primary cause of the other regulatory shifts in carbon metabolism seen with ammonia (and now with methylamine) as has been proposed earlier. Stimulation of phosphoenolpyruvate carboxylase by methylamine supports a previous proposal that the activity of this enzyme increases with a small rise in cytoplasmic pH resulting from entry of ammonia into the cytoplasm. Increases in the activity of pyruvate kinase and the rate of oxidation of triose phosphate remain unexplained. If these changes are due to change in ATP/ADP ratio, the cause for the change in this ratio must be found elsewhere than in a stimulation of the rate of glutamine synthesis.
日本植物生理学会の論文