The biosynthesis of kojic acid. 4. Production from pentoses and methyl pentoses

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Abstract
The 8 stereosiomeric pentoses were used as substrates for Aspergillus flavus. D-Ribose and D-xylose give the highest yields of kojic acid; L-arabinose is less effective and D-arabinose, D-lyxose, and L-xylose are very poor C sources for kojic acid formation. A. flavus did not form kojic acid from L-lyxose or L-ribose, and these two pentoses varely support growth of this organism. In replacement cultures using mycelia pregrown on glucose, only D-ribose and D-xylose are good sources for continued kojic acid production. Of the two methyl pentoses tested, L-fucose does not support the growth of either A. flavus or A. oryzae. L. Rhamnose is a fairly good C source for kojic acid formation by A. flavus. With D-(1-C14) ribose as a substrate for A. flavus, the radioactivity of the respiratory CO2 was low initially and increased to a maximum at the 3d day. Of the radioactivity of kojic acid isolated from this culture, 80% was contained in C atoms, 1,2, and 3. This distribution pattern indicates a conversion of ribose into the Cg precursor by the transketolase and transaldolase reactions. Further oxidation of the C6 precursor is believed to account for the radioactivity in C atom 2 or the kojic acid. The relationship of these observations to the previously postulated pathways of kojic acid formation from glucose and small molecules is discussed.