The enzymatic conversion of 5-dehydroshikimic acid to protocatechuic acid.

Previous studies of the physiology of an aromatic-deficient mutant strain of Neurospora crassa, Y7655a (1, 2), have led to the following conclusions: (a) The biosynthesis of the aromatic rings of phenylalanine, tyrosine, tryptophan and p-aminobenzoic acid proceeds in Neurospora as it does in Escherichia coli (3) via 5-dehydroshikimic acid and shikimic acid. (b) Protocatechuic acid, the major compound secreted by the mutant strain during growth, is derived from DHS’ (I). (c) The observed distributions of carbon atoms 1 and 6 of glucose into PCA was compatible with the notion that the aromatic ring structure was derived by the condensation of a 3and a 4-carbon fragment derived from glucose (2). (d) A comparison of the results obtained for the distribution of carbon atoms 1 and 6 of glucose into shikimic acid accumulated by a mutant strain of E. coli (4) with the distribution obtained in PCA accumulated by Neurospora led to the assumption that the conversion of DHS to PCA in Neurospora involved the loss of the carbonyl oxygen atom at position 5 of DHS (2). This report primarily concerns the enzymat.ic conversion of DHS to PCA. Evidence is presented indicating that this conversion does not involve the loss of the carbonyl oxygen atom at position 5 of DHS, but instead is a result of a dehydration in which the hydroxyl oxygen atom at position 3 is lost. Some properties of the enzyme responsible for this conversion, dehydroshikimic dehydrase, are described.