Biosynthesis of Vitamin B6

The biosynthesis of vitamin B6 was studied in an Escherichia coli mutant, blocked between pyridoxol and pyridoxal. Specific incorporation of glycerol, pyruvate, serine, and glucose was shown by chemical degradation of labeled samples of pyridoxol isolated from the medium of cultures which had been incubated with various 14C-labeled radiomers of these substrates. The observed pattern of incorporation of 14C shows that pyridoxol is derived from 3 triose units. One of these is incorporated by way of pyruvate, as a 2-carbon unit at the oxidation level of acetaldehyde. The other 2 triose units are incorporated intact. A hypothetical sequence for the biogenesis of pyridoxol is advanced on the basis of the tracer evidence. 5-Deoxyxylulose 1-phosphate and a branched chain 8-carbon sugar are postulated as intermediates.