Catechol oxygenases of Pseudomonas putida mutant strains

Benzoate and muconate, structurally dissimilar metabolites, induce expression of catA in Acinetobacter calcoaceticus

Biosynthetic regulation of catA, the gene encoding catechol 1,2-dioxygenase (EC 1.13.1.1), was studied in an Acinetobacter calcoaceticus mutant strain unable to metabolize benzoate. Benzoate and muconate independently induced the enzyme. In glucose-grown cells, benzoate yielded higher enzyme levels than did muconate, whereas muconate was the more effective inducer in succinate-grown cells.

Control of catechol meta-cleavage pathway in Alcaligenes eutrophus

Alcaligenes eutrophus 335 (ATCC 17697) metabolizes phenol and p-cresol via a catechol meta-cleavage pathway. Studies with mutant strains, each defective in an enzyme of the pathway, showed that the six enzymes assayed are induced by the primary substrate. Studies with a putative polarity mutant defective in the expression of aldehyde dehydrogenase suggested that the structural genes encoding this and subsequent enzymes of the pathway exist in the same operon. From studies with mutant strains that constitutively synthesize catechol 2,3-oxygenase and subsequent enzymes and from the coordination of repression of these enzymes by p-toluate, benzoate, and acetate, it is proposed the catechol 2,3-oxygenase structural gene is situated in this operon (2,3-oxygenase operon). Studies with regulatory mutant strains suggest that the 2,3-oxygenase operon is under negative control.

Evidence for isofunctional enzymes used in m-cresol and 2,5-xylenol degradation via the gentisate pathway in Pseudomonas alcaligenes

Study of the reaction sequence by which Pseudomonas alcaligenes (P25X1) and derived mutants degrade m-cresol, 2,5-xylenol, and their catabolites has provided indirect evidence for the existence of two or more isofunctional enzymes at three different steps. Maleylpyruvate hydrolase activity appears to reside in two different proteins with different specificity ranges, one of which (MPH1) is expressed constitutively; the other (MPH11) is strictly inducible. Two gentisate 1,2-dioxygenase activities were found, one of which is constitutively expressed and possesses a broader specificity range than the other, which is inducible. From oxidation studies with intact cells, there appear to be two activities responsible for the 6-hydroxylation of 3-hydroxybenzoate, and again a broadly specific activity is present regardless of growth conditions; the other is inducible by 3-hydroxybenzoate. Three other enzyme activities are also detected in uninduced cells, viz., xylenol methylhydroxylase, benzylalcohol dehydrogenase, and benzaldehyde dehydrogenase. All apparently possess broad specificity. Fumarylpyruvate hydrolase was also detected but only in cells grown with m-cresol, 3-hydroxybenzoate, or gentisate. Mutants, derived either spontaneously or after treatment with mitomycin C, are described, certain of which have lost the ability to grow with m-cresol and 2,5-xylenol and some of which have also lost the ability to form the constitutive xylenol methylhydroxylase, benzylalcohol dehydrogenase, benzaldehyde dehydrogenase, 3-hydroxybenzoate 6-hydroxylase, and gentisate 1,2-dioxygenase. Such mutants, however, retain ability to synthesize inducibly a second 3-hydroxybenzoate 6-hydroxylase and gentisate 1,2-dioxygenase, as well as maleylpyruvate hydrolase (MPH11) and fumarylpyruvate hydrolase; MPH1 was still synthesized. These findings suggest the presence of a plasmid for 2,5-xylenol degradation which codes for synthesis of early degradative enzymes. Other enzymes, such as the second 3-hydroxybenzoate 6-hydroxylase, gentisate 1,2-dioxygenase, maleylpyruvate hydrolase (MPH1 and MPH11), and fumarylpyruvate hydrolase, appear to be chromosomally encoded and, with the exception of MPH1, strictly inducible.

Mutants defective in isomerase and decarboxylase activities of the 4-hydroxyphenylacetic acid meta-cleavage pathway in Pseudomonas putida

Degradation of 2-hydroxy-5-carboxymethylmuconic semialdehyde, the ring fission product of the 4-hydroxyphenylacetate meta-cleavage pathway, by mutant strains P23X19 and P23X16 of Pseudomonas putida NCI B 9865 was studied. Both mutants were unable to grow on either 4-hydroxyphenylacetate of 3,4-dihydroxyphenylacetate. Cell extracts of P23X19, grown in the presence of 3,4-dihydroxyphenylacetate, degraded the ring fission product to a compound that accumulated and had maximum UV absorption at 300 nm, pH 7.4, and 345 nm, pH 12. These are the spectral characteristics of 2-keto-5-carboxymethylhex-3-ene-1,6-dioate, the substrate for the decarboxylase in this pathway. This observation is consistent with P23X19's being decarboxylase defective. Cell extracts of P23X16, grown in the presence of 3,4-dihydroxyphenylacetate, degraded the ring fission product to a compound that accumulated and has maximum UV absorption at 295 nm, pH 7.4, and 345 nm, pH 12. This compound spontaneously degraded to a compound with the spectral properties of the decarboxylase substrate. The compound accumulated by P23X16 was also obtained when the decarboxylase substrate was treated with borate. It is suggested that the compound accumulated by P23X16 is the substrate of an isomerase. The results are consistent with P23X16's being unable to synthesize a functional isomerase while retaining decarboxylase activity and establish the physiological importance of an enzyme-catalyzed isomerization in the meta-cleavage degradation of 4-hydroxyphenylacetate.