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Some nutritive aspects of proteinase biosynthesis by non-proliferating cells of Streptococcus liquefaciens, strain 31, were investigated by substituting constituents in a basal medium containing casein, lactose, purines, pyrimidines, vitamins, and salts. The casein of the medium could be replaced by a mixture of 12 "essential" amino acids (glutamic acid, histidine, valine, serine, methionine, leucine, isoleucine, arginine, cystine, lysine, tryptophane, and threonine), thus demonstrating that proteinase synthesis can occur in a medium devoid of protein. Proteinase biosynthesis appeared to depend upon an inordinately high concentration of arginine, required a fermentable carbohydrate, and occurred optimally at pH 6.3. Sodium fluoride and iodoacetate did not inhibit the proteinase activity but radically curbed its synthesis.

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One of the most perplexing problems of intermediary metabolism has been the nature of the mechanism by which some microbial cells derive all the energy they need, and synthesize the complex substances which they require, from compounds containing only two carbon atoms. One key to the solution of this problem was an understanding of how acetate was metabolized by such cells. For over 50 years, since Harden (1) suggested that two molecules of acetate condensed to form succinate, the enigma was never satisfactorily resolved. Harden's suggestion was later incorporated in a scheme, the Thunberg-Knoop dicarboxylic acid cycle (2), which seemed to account for a number of biochemical events related to the metabolism of acetate in bacteria. There was increasing evidence by 1955 that bacteria could also use the Krebs tricarboxylic acid cycle (3) for the same purpose. The net result of both mechanisms was complete oxidation of acetate to carbon dioxide and water. But the differences in the requirements of the two cycles to achieve the same result frustrated attempts to reconcile observations and theories into a unified concept acceptable to all workers. The pitfalls which impeded progress on this problem have been reviewed by Ajl (4), Elsden (5), and Kornberg (6).The discoveries of isocitrate lyase by Olson (7) in 1954 and malate synthase by Wong and Ajl (8) in 1956 were crucial in the ultimate resolution of the problem. These two enzymes, acting in concert, form a cyclic mechanism, the glyoxylate bypass (9). The bypass provides an efficient means by which the cell can synthesize one mole 1548 of succinate from two moles of acetate, and thus serves to replenish the tricarboxylic acid cycle with four-carbon acids drained from the cycle during cellular biosynthesis. Reviews by Ajl (4), Krampitz (10), Krebs and Lowenstein (11), and Kornberg and Elsden (12) summarize this research and form a foundation for the work to be discussed here.Several years ago a new and challenging aspect of intermediary metabolism became apparent when efforts in our laboratory were directed toward answering the question: Are there enzymes which catalyze the condensation of glyoxylate with short-chain fattyacid esters of coenzyme-A (CoA) other than acetyl-CoA? If so, what products are formed, how are they metabolized, and what function do they have in bacterial physiology? Condensation with Propionyl-CoA