Phenylalanine-Tyrosine Biosynthesis in NEUROSPORA CRASSA.

IOCHEMICAL investigations of the phenylalanine-tyrosine specific portion of the aromatic pathmway reveal a reaction sequence depicted in Figure 1. Although the organisms studied use similar intermediates to accomplish phenylalanine and tyrosine synthesis, some important functional differences exist. Aerobacter aerogenes and Escherichia coli W possess two molecular forms of chorismate mutase separable by chromatography on DEAE-cellulose (COTTON and GIBSON 1965). One (CM-T) is associated with prephenate dehydrogenase activity and the other (CM-P) is associated with prephenate dehydratase activity. The activities of the CM-T aggregate are feedback-inhibited by tyrosine and activities of the CM-P aggregate are inhibited by phenylalanine. In each case the two associated activities can be affected simultaneously by one mutational event. Similar results have been reported for E. coli K12 (PITTARD and WALLACE 1966). Bacillus subtilis produces three molecular species of chorismate mutase (LORENCE and NESTER 1967). No stable association with subsequent enzymes in phenylalanine or tyrosine synthesis occurs, but chorismate mutase activity and 3-deoxy-D-arabino-heptulosonic acid-7-phosphate (DAHP) synthetase activity does occur in a single aggregate in this organism (NESTER, LORENCE and NASSER