A Bifunctional Enzyme in Pseudomonas aeruginosa : a New Pattern in the Organization of Enzymes Concerned with Phenylalanine and Tyrosine Biosynthesis

Abstract

Two isozymes of chorismate mutase (CA mutase 1 and CA mutase 2 ) and two isozymes of prephenate dehydratase (PPA dehydratase 1 and PPA dehydratase 2 ) have been found in Pseudomonas aeruginosa . The activities CA mutase 2 -PPA dehydratase 2 catalyzing phenylalanine biosynthesis have been purified almost 40-fold and were found to be associated as a bifunctional enzyme or an enzyme complex. The enzymes specific for tyrosine biosynthesis did not appear to manifest such physical association. Thus, the organization of enzymes concerned with phenylalanine and tyrosine biosynthesis in P. aeruginosa is unique and is unlike most other organisms. Single site mutants have been isolated which have lost both CA mutase 2 -PPA dehydratase 2 activities resulting in a requirement for phenylalanine for growth. Single site revertants of these mutants regained both these activities simultaneously and were able to grow on minimal medium. A mutant, r 6 , was also isolated which had normal CA mutase 2 but lacked PPA dehydratase 2 activity.