Glyoxylic acid carboligase: an enzyme present in glycolate-grown Escherichia coli.

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 Escherichia coli grown on acetate. These data cannot be readily explained by the glyoxylic acid by-pass pathway. In 1956, we (Krakow and Barkulis) reported briefly that extracts obtained from E. coli Crookes strain, which had been grown with glycolate as the only carbon source, could form either hydroxypyruvate or tartronic semialdehyde from glyoxylate under anaerobic conditions. The formation of these 3-carbon compounds from a