PHHC IS AN ESSENTIAL AMINOTRANSFERASE FOR AROMATIC AMINO-ACID CATABOLISM IN PSEUDOMONAS-AERUGINOSA

The phhC gene of Pseudomonas aeruginosa encodes a protein which is a m ember of the Family I aminotransferases, At high expression levels in the heterologous Escherichia coil system, PhhC can compensate for the absence of AspC (which functions in L-aspartate biosynthesis) and TyrB (which functions in aromatic biosynthesis). In the native organism, P hhC is essential for catabolism of either L-tyrosine or L-phenylalanin e, as demonstrated by gene inactivation. This catabolic function of Ph hC is consistent with its inclusion as the distal gene in the inducibl e phenylalanine hydroxylase operon. The presence of PhhC for catabolis m of aromatic amino acids is required in spite of an existing multipli city of other P. aeruginosa aminotransferases having a similar pattern of broad substrate specificity in vitro. This implies a spatial orien tation of PhhC that effectively specializes it for aromatic amino acid catabolism.