The Conversion of Shikimic Acid to Anthranilic Acid by Extracts of Neurospora Crassa.

The role of shikimic acid as a common intermediate in the synthesis of phenylalanine, tyrosine, tryptophan, and p-aminobenzoic acid has been recognized for some time (l-3). The enzymes which catalyze the synthesis of shikimic acid from intermediates of carbohydrate metabolism have been observed in extracts of bacteria (4-6) as well as Neurospora crassa (7). On the other hand, the reactions leading from shikimic acid to specific intermediates in the synthesis of the various aromatic amino acids have been poorly understood. Only recently, studies with extracts from bacterial mutants (S-13) have implicated the sequence of reactions presented in Fig. 1. From the bacterial studies, it appears that shikimic acid is converted by three enzymatic reactions to chorismic acid, which serves as a direct precursor of the various specific pathways of aromatic biosynthesis. Genetic and nutritional studies with N. crassa indicate that the first enzyme specifically involved in tryptophan biosynthesis catalyzes the formation of anthranilic acid (14). As an initial approach toward the investigation of this enzyme in N. crassa, attempts were made to show the conversion of shikimic acid to anthranilic acid. Under the conditions employed in the bacterial studies, crude extracts of N. crassa did not catalyze this conversion. The studies presented here were undertaken to define the conditions necessary for the synthesis of anthranilic acid from shikimic acid in N. crassa and to investigate the reactions involved.