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Role of Vitamin B₆ Biosynthetic Rate in the Study of Vitamin B₆ Synthesis in Escherichia coli

¹ Microbial and Medical Genetics Unit, Veterans Administration Hospital, and Department of Biochemistry, University of Texas Southwestern Medical School, Dallas, Texas 75216

ABSTRACT

Nutritional auxotrophs of Escherichia coli synthesize vitamin B₆ compounds at a rate of 1 x 10^–10 to 2 x 10^–10 moles per hr per mg (dry weight) of cells when they are suspended in minimal medium lacking their required nutrients. A few auxotrophs have been found to stop or reduce vitamin B₆ synthesis during such an experiment. These include thiamineless, citrate synthaseless, and pyridoxineless mutants as well as mutants which require four carbon compounds for growth. Glycolaldehyde was found to restore vitamin B₆ synthesis in the last named of these mutants without restoring normal growth. A class of pyridoxineless mutants which responded with normal growth to 0.4 mM glycolaldehyde or 0.15 x 10^–3 mM pyridoxol was also found. The results suggest that a thiamine pyrophosphate-requiring step as well as glycolaldehyde may be involved in pyridoxal phosphate biosynthesis.

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