A DIRECT SULFHYDRYLATION PATHWAY IS USED FOR METHIONINE BIOSYNTHESIS IN PSEUDOMONAS-AERUGINOSA

The relationship between genes and enzymes in the methionine biosynthe tic pathways has been studied in Pseudomonas aeruginosa. The first ste p is catalysed by an O-succinylhomoserine synthase,. the product of th e metA gene mapped at 20 min on the chromosome. The second step is ach ieved by direct sulfhydrylation, involving the enzyme encoded by a met Z gene that we have identified and sequenced, located at 40 min. Thus Pseudomonas appears to be the only organism so far described that uses O-succinylhomoserine as substrate for a direct sulfhydrylation. As in yeast, the two transsulfuration pathways between cysteine and homocys teine, with cystathionine as an intermediate, probably exist in parall el in this organism.