Protein-protein interactions and antigenic relationships between the components of 4-methoxybenzoate monooxygenase and of benzene 1,2-dioxygenase from Pseudomonas putida

Mechanistic and stereochemical studies of a unique dehydration catalyzed by CDP-4-keto-6-deoxy-D-glucose-3-dehydrase: a pyridoxamine 5'-phosphate dependent enzyme isolated from Yersinia pseudotuberculosis

CDP-4-keto-6-deoxy-D-glucose-3-dehydrase (E1) purified from Yersinia pseudotuberculosis is a pyridoxamine 5'-phosphate (PMP) dependent enzyme which catalyzes the C-O bond cleavage at C-3 of a CDP-4-keto-6-deoxy-D-glucose substrate, a key step in the formation of 3,6-dideoxyhexoses. Since enzyme E1 utilizes the PMP cofactor in a unique manner, it is essential to establish its role in E1 catalysis. When an incubation was conducted in [18O]H2O, incorporation of 18O into positions C-3 and C-4 of the recovered substrate was observed. This result not only provided the evidence necessary to reveal the reversibility of E1 catalysis but also lent credence to the formation of a delta 3,4-glucoseen intermediate. In view of E1 catalysis being initiated by a C-4' deprotonation of the PMP-substrate complex, the stereochemical course of this step was examined using chemically synthesized (4'S)- and (4'R)-[4'-3H]PMP as probes. Our results clearly demonstrated that the stereochemistry of this deprotonation is pro-S specific, which is in agreement with the stereochemical consistency found with other vitamin B6 phosphate dependent enzymes. The fact that reprotonation at C-4' of the PMP-delta 3,4-glucoseen complex in the reverse direction of E1 catalysis was also found to be pro-S stereospecific strongly suggested that enzyme E1, like most of its counterparts, has the si face of its cofactor-substrate complex exposed to solvent and accessible to active-site catalytic groups as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Substrate-modulated reactions of putidamonooxin. The nature of the active oxygen species formed and its reaction mechanism

1. 4-Methoxybenzoate monooxygenase is fairly nonspecific. The enzyme system with putidamonooxin as its oxygen-activating component catalyses: (a) O-, S- and N-demethylation; (b) the oxygenation of 4-methylbenzoate and 4-methylmercaptobenzoate, with formation of 4-carboxybenzyl alcohol and 4-carboxyphenylmethyl sulfoxide, respectively, and (c) attack of the aromatic ring of 4- and 3-hydroxybenzoate and 4-aminobenzoate, yielding 3,4-dihydroxybenzoate and 4-amino-3-hydroxybenzoate, respectively. 2. Compounds which are bound by the active sites of putidamonooxin have two essential features in common: a planar aromatic ring system, and a free carboxyl group attached to it. 3. By a substrate-modulated reaction putidamonooxin can be induced to function not only as a monooxygenase but also as a peroxotransferase, i.e. it incorporates both atoms of the activated oxygen molecule into a substrate molecule. This finding supports the hypothesis that a mesomeric state of the iron.peroxo complex, [FeO2]+, is indeed the active oxygenating species of putidamonooxin. 4. The lifetime of the ternary complex consisting of enzyme.iron-peroxo-complex.substrate is significantly prolonged by uncoupling and partially uncoupling substrates, except when it is inactivated by protonation of the iron.peroxo complex by a proton transported into the active sites by a special kind of substrate (i.e. isomers of monoaminobenzoate), with the direct formation of H2O2. 5. The lifetime of the active oxygen species is determined by (a) the rate of the oxygenation reaction in the presence of tight-coupling substrates and (b) the rate of the oxygenation reaction as well as detoxification by the availability of a dissociable proton in the presence of partial uncoupling (and uncoupling) substrate analogues. 6. The rate of the oxygenation reaction depends on the lifetime of the active oxygen species, [FeO2]+, in the presence of partial uncoupling substrates. 7. The iron.peroxo complex attacks an aromatic ring system according to the empiric rules of electrophilic substitution, whereas the attack of aliphatic substituents at the aromatic ring is controlled by steric criteria.

Benzene dioxygenase in Pseudomonas putida. Subunit composition and immuno-cross-reactivity with other aromatic dioxygenases

The terminal oxygenase component of benzene dioxygenase from Pseudomonas putida strain ML2 was shown to contain two subunits, of Mr 54,500 and 23,500, by SDS/polyacrylamide-gel electrophoresis. The native Mr of the terminal oxygenase was estimated to be 168,000 +/- 4000. Polyclonal antibodies raised against each of the subunits cross-reacted with two polypeptides in cell-free extracts from toluene-grown Pseudomonas putida strain N.C.I.B. 11767. The Mr values of these polypeptides were similar to those reported for the subunits from the terminal dioxygenase component of toluene dioxygenase. These polypeptides were present only when this strain was grown on toluene. No cross-reactivity was observed with subunits of the naphthalene dioxygenase or benzoate dioxygenase systems.