The Assimilation of Glutamic Acid by Yeast

Abstract

Using the corresponding amino acid decarboxylases, arginine, glutamic acid, histidine, lysine, ornithine and tyrosine were found to be free inside the cells of yeast. They are present when growth takes place in the absence of amino acids, but their concn. may be increased by growing the organisms in media rich in amino acids. Uptake of glutamic acid from the external medium is dependent on a source of energy which can be provided by the simultaneous fermentation of glucose. The presence of an ammonium salt in the medium decreases both the rate at which glutamic acid enters the cells and the amt. of glutamic acid which can be taken up. Certain other amino-acids exert a similar sparing action on the assimilation of glutamic acid, which can be related to their efficiency as N sources for growth. The free glutamic acid content of cells remains practically constant when the cells are suspended in salt solns. without amino acids, but if glucose is also present, then the concn. of free glutamic acid inside the cells decreases steadily. When ammonia is also present the concn. of glutamic acid remains constant, suggesting that glutamic acid is synthesized by the cells under these conditions, or alternatively that the ammonia is assimilated and utilized preferentially.