Abstract
Dempsey, Walter B. (University of Florida, Gainesville). Control of pyridoxine biosynthesis in Escherichia coli J. Bacteriol. 90:431–437. 1965.—The total pyridoxine in a culture of exponentially growing Escherichia coli was 3.6 × 10−10 moles per mg of dry cells. One-fourth of this total was present in the medium, and was at least 90% pyridoxal 5′-phosphate. Both pyridoxol and pyridoxal, when present initially at 6 × 10−7m, substituted entirely for de novo synthesis of pyridoxine. The other four forms of the pyridoxine group were ineffective at this concentration. Pyridoxine biosynthesis in exponentially growing cultures of E. coli was immediately stopped by adding pyridoxol to the medium to a final concentration of 4 × 10−7m. Amino acid auxotrophs of E. coli suspended in minimal medium without the required amino acid produced extracellular pyridoxine for several hours at an average rate of 1.3 × 10−10 moles per hr per mg of dry cells. The rate of production of extracellular pyridoxine by a threonine-starved threonine auxotroph was not altered by growing the culture before starvation in media containing 6 × 10−5m pyridoxol. The extracellular form of pyridoxine produced in these starvations required hydrolysis to be detected in the bioassay used in these measurements. The total findings suggest that pyridoxine biosynthesis is controlled by a rapidly acting mechanism but not by repression.
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