Role of Vitamin B₆Biosynthetic Rate in the Study of Vitamin B₆Synthesis inEscherichia coli

Abstract

Nutritional auxotrophs of Escherichia coli synthesize vitamin B 6 compounds at a rate of 1 × 10 −10 to 2 × 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 B 6 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 B 6 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 m m glycolaldehyde or 0.15 × 10 −3 m m pyridoxol was also found. The results suggest that a thiamine pyrophosphate-requiring step as well as glycolaldehyde may be involved in pyridoxal phosphate biosynthesis.

Glycolaldehyde Is a Precursor of Pyridoxal Phosphate in Escherichia coli B

“…That pyridoxal phosphate biosynthesis directly involves the addition of a two-carbon unit is one interpretation both of the data presented here and of our previous finding that completely thiamineless E. coli stop synthesis of vitamin B, upon thiamine starvation (6). Glycolaldehyde could enter B6 biosynthesis as either donor or acceptor of a two-carbon unit from a transketolase.…”

“…The synthetic glycolaldehyde was identified by its ability to substitute for commercially prepared glycolaldehyde in feeding the pyridoxineless E. coli strain WG3. Glycolaldehyde had previously been shown to substitute for pyridoxine in this strain (6). A typical response curve is shown in Fig.…”

“…The strain used was E. coli B strain WG3 (pdxB3). It is a pyridoxineless strain (5) which can use glycolaldehyde to replace its pyridoxine requirement (6). The position of' the pdxB3 gene on the chromosomal map of E. coli has been established at 45 min (4).…”

“…The problem has been attacked in Escherichia coli by several investigators using widely differing techniques such as bacterial genetics, physiology (2-6, 15, 16), and classical bioorganic chemistry (10)(11)(12). The former studies have identified a number of different groups of pyridoxine auxotrophs (3,4) which have suggested that glycolaldehyde (6,15,16) and serine phosphate (2), and possibly glutamate (6) are intermediates in pyridoxine biosynthesis. Presently, no unequivocal evidence has appeared which supports any of the above compounds as intermediates.…”

“…We did this by examining a large number of pyridoxineless mutants of E. coli B which had been isolated after ultraviolet light-induced mutagenesis for a class of mutants which had a single nutritional requirement for pyridoxine which could be satisfied by glycolaldehyde. We found such a class of mutants (6) and tested the incorporation of glycolaldehyde with it.…”