The dissimilation of amino acids by Rhodospirillum rubrum

anaerobically in the light and incubated in the light under argon metabolized many of the 15 amino acids tested and produced ammonia and carbon dioxide as the prin-cipal extracellular products. Hydrogen was also produced in the presence of glutamic acid. Of the glutamic acid metabolized 80 yo of the carbon and 55-70 yo of the nitro-gen were converted into intracellular products. The magnitude of the catabolism of the other amino acids, as measured by ammonia and carbon dioxide production, appears to be an inverse function of the closeness to which the elemental composition of the amino acid approximates to that of cell material. When the organism was grown aerobically in the dark, studies of the metabolism of amino acids by washed suspensions, under aerobic conditions, were complicated by the relatively high rate of endogenous respiration. In the presence of certain amino acids this was decreased by 9 yo (with alanine) to 45 yo (with aspartic acid), and glutamic acid, aspartic acid and alanine, a t least, were oxidized to completion by the organism. Although Rhodospirillum rubrum can utilize amino acids as sole hydrogen donor and nitrogen source for growth, no systematic studies on its amino acid metabolism have been published as far as the author is aware. The work de-scribed in this paper is the first part of an attempt to ' elucidate the mechanism of amino acid metabolism by washed suspensions of the organism when grown under anaerobic conditions in the light or under aerobic conditions in the dark. Hereafter suspensions grown under these two conditions will be referred to a