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A number of metabolic reactions have been shown to occur in microorganisms in recent years, which help to explain their ability to utilize 2-carbon compounds for growth. The central reaction for acetate-grown organisms appears to be the malic synthetase described by Wong and Ajl (1956, 1957) in which a 4-carbon compound, malic acid, is synthesized from acetyl coenzyme A (CoA) and glyoxylic acid. Other adaptive enzymes, such as citritase (Dagley and Dawes, 1953; Gillespie and Gunsalus, 1953) and isocitritase (Campbell, Smith, and Eagles, 1953; Smith and Gunsalus, 1954, 1957), are found in acetate-grown organisms. Kornberg and Krebs (1957) have proposed the name "glyoxylic acid by-pass" for the isocitritase-malic synthetase enzymes acting in concert to provide carbon substrates feeding into the tricarboxylic acid cycle. Nonetheless, this may be only one of a number of ways in which acetate-grown organisms synthesize larger carbon compounds. Glasky and Rafelson (1959), measuring the incorporation of C14-acetate into various compounds by a method similar to that of Calvin and co-workers (1950), have found that succinate is formed prior to malate and isocitrate in the Crookes strain of

The stereospecificity of hydrogen transfer for the pyridine nucleotide has been ascertained for a number of hitherto uninvestigated dehydrogenase reactions. These determinations have been made with the help of appropriate reference enzymes, and of DPN and TPN labeled with tritium at the 4 position of the nicotinamide ring. Evidence is presented that the following enzymes use the same position (i.e., A or a) as yeast alcohol dehydrogenase: DPN-linked formic dehydrogenase from pea seeds, DPN-linked glyoxylic reductase from spinach leaves, TPN-linked glyoxylic reductase from pea seeds, TPN-linked dihydroorotic dehydrogenase from an aerobic bacterium, and TPN-linked malic enzyme from liver. The opposite stereospecificity (B or ß) is demonstrated for the DPN-linked liver dehydrogenase which oxidizes uridine diphosphoglucose to uridine diphosphoglucuronic acid.

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