Control of meta-cleavage degradation of 4-hydroxyphenylacetate in Pseudomonas putida

Synthesis of enzymes of the 4-hydroxyphenylacetate meta-cleavage pathway was studied in Pseudomonas putida wild-type strain P23X1 (NCIB 9865) and mutant strains which had either structural or regulatory gene mutations. Induction studies with mutant strains each defective in an enzyme of the pathway showed that 4-hydroxyphenylacetate induced the hydroxylase and that 3,4-dihydroxyphenylacetate induced the 2,3-oxygenase, aldehyde dehydrogenase, isomerase, decarboxylase, and hydratase. This showed that the hydroxylase structural gene does not exist in an operon that contains any other structural gene of this meta pathway. Studies of mutant strains that synthesized constitutively the 2,3-oxygenase and subsequent enzymes suggested that the regulation of synthesis of these enzymes was coincident, and, in such strains, the hydroxylase was inducible only. Observations made with a putative polarity mutant that lacked 2,3-oxygenase activity suggested that the structural genes encoding this enzyme and subsequent enzymes of the pathway exist in the same operon. Studies of a regulatory mutant strain that was defective in the induction of the 2,3-oxygenase and subsequent enzymes suggest that the 2,3-oxygenase operon is under positive control.