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W McIntire

Publications and source records attributed to W McIntire.

At least 19 recordsLinked to original sources
PubMed1986

Amino acid and sequence analysis of the cytochrome and flavoprotein subunits of p-cresol methylhydroxylase.

The flavocytochrome p-cresol methylhydroxylase from Pseudomonas putida has been reported to have a Mr of 114,000 and to consist of two subunits, a flavoprotein and a cytochrome c, each with a Mr of 58,000. Recent X-ray crystallographic data from our laboratories [Shamala, N., Lim, L. W., Mathews, F. S., McIntire, W., Singer, T. P., & Hopper, D. J. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 4626-4630], however, indicate an alpha 2 beta 2 structure and a much lower molecular mass (approximately 8000) for the cytochrome subunit. In this paper we report data confirming the conclusions of X-ray crystallographic analysis. From quantitative amino acid analysis, the molecular mass of the flavoprotein monomer is shown to be 48,600 +/- 2200 and that of the cytochrome 8780 +/- 250. These values have been confirmed by gel electrophoresis under denaturing conditions. Gel chromatography under nondenaturing conditions shows that the isolated flavoprotein exists as a dimer, whereas the isolated cytochrome is a monomer. The complete amino acid sequence of the cytochrome c subunit is presented and is shown to have regions of homology to other bacterial c-type cytochromes. The partial N-terminal amino acid sequence (56 amino acids) of the flavoprotein subunit is also reported. The implications of the now established tetrameric structure of the flavocytochrome on data in the literature regarding the redox and association properties of the subunits are examined.

Amino Acid Sequence↗
PubMed1986

Structure of an intermolecular electron-transfer complex: p-cresol methylhydroxylase at 6.0-A resolution.

The structure of p-cresol methylhydroxylase [4-cresol:(acceptor) oxidoreductase (methyl-hydroxylating), EC 1.17.99.1], a flavocytochrome c, has been determined at 6.0-A resolution. The structure analysis is based on two heavy-atom derivatives with anomalous scattering and 2-fold averaging about a noncrystallographic axis. The molecule is an alpha 2 beta 2 tetramer with a cytochrome subunit of Mr approximately 8500 and a flavoprotein subunit of Mr approximately 49,000. The flavoprotein subunits are tightly packed about the molecular 2-fold axis, whereas the cytochrome subunits are located on the outside of the molecule, each in a depression on the surface of a flavoprotein subunit. The results of this study have led to the following conclusions. The alpha 2 beta 2 quaternary structure of the enzyme is different from alpha beta as originally thought. The orientation of the cytochrome subunit and the surface complementarity of the cytochrome and flavoprotein subunits are clearly defined. The cytochrome subunit is similar in size to other small bacterial cytochromes but probably forms a distinct subclass. The titration (by substrate) behavior of the enzyme and other kinetic properties are rationalized by its quaternary structure.

Bacterial Proteins↗
PubMed1985

Identification of the covalently bound flavins of D-gluconate dehydrogenases from Pseudomonas aeruginosa and Pseudomonas fluorescens and of 2-keto-D-gluconate dehydrogenase from Gluconobacter melanogenus.

An improved method is presented for the purification of 8 alpha-(N1-histidyl)riboflavin, 8 alpha-(N3-histidyl)riboflavin and their 2',5'-anhydro forms, which permits the isolation of sizeable quantities of each of these compounds from a synthetic mixture in pure form. Flavin peptides were isolated from the D-gluconate dehydrogenases of Pseudomonas aeruginosa and Pseudomonas fluorescens and from the 2-keto-D-gluconate dehydrogenase of Gluconobacter melanogenus. After conversion into the aminoacyl-riboflavin, the flavin in all three enzymes was identified as 8 alpha-(N3-histidyl)riboflavin. By sequential treatment with nucleotide pyrophosphatase and alkaline phosphatase, the flavin in each enzyme was shown to be in the dinucleotide form.

Carbohydrate Dehydrogenases↗
PubMed1985

Resolution of the flavocytochrome p-cresol methylhydroxylase into subunits and reconstitution of the enzyme.

An improved procedure is described for the isolation of the flavocytochrome p-cresol methylhydroxylase (PCMH) from Pseudomonas putida as well as methods for the separation of its subunits in native form and their recombination to reconstitute the original flavocytochrome. Under appropriate conditions, the reconstitution is stoichiometric and results in complete recovery of the catalytic activity of the flavocytochrome. The separated flavoprotein subunit shows only 2% of the catalytic activity of the original enzyme on p-cresol and is characterized by converging lines in bisubstrate kinetic analysis, while the intact and reconstituted enzymes show parallel line kinetics in steady-state experiments. van't Hoff plots of the dependence of the dissociation constant of the subunits of PCMH on temperature show a break near 15 degrees C. Above this temperature, KD is characterized by a positive delta H value of 12.6 kcal mol-1; below 15 degrees C, the dissociation is essentially temperature independent. The subunit dissociation is strongly dependent on ionic strength in the oxidized form of PCMH but not in the reduced form of the enzyme. Reduction also lowers the KD significantly, while substrates and nonoxidizable competitive inhibitors lower the dissociation constant even further, suggesting a conformation change. Combination of the subunits to form PCMH entails a small but measurable change in the absorption spectra of the component proteins.

Isoelectric Focusing↗
PubMed1985

p-Cresol methylhydroxylase. Assay and general properties.

p-Cresol methylhydroxylase from Pseudomonas putida, an anaerobic dehydrogenase that catalyses the oxidation of p-cresol to p-hydroxybenzyl alcohol and then to p-hydroxybenzaldehyde, is an enzyme of great interest in several respects. One of these is the fact that its flavoprotein and cytochrome c subunits may be reversibly dissociated with ease, with full regeneration of the activity and its native properties on recombining the components. Bisubstrate kinetic analysis of the unresolved enzyme gives parallel-line kinetics in double-reciprocal plots, whereas the reaction of the separated flavoprotein subunit with substrates is described by converging lines. The mechanistic implications of these behaviours are discussed. Reductive titration with dithionite results in the uptake of 3 electrons by the enzyme, with the intermediate formation of the anionic flavin radical [McIntire, Edmondson, Hopper & Singer (1981) Biochemistry 20, 3068-3075]. Reductive titration with substrates resulted initially only in reduction of the cytochrome subunit, followed by formation of the anionic radical and finally the fully reduced enzyme. These observations suggest rapid intermolecular electron transfer between p-cresol methylhydroxylase molecules. This paper also examines the effect of pH and ionic strength on the activity and specificity of the enzyme with respect to substrates and natural, as well as artificial, electron acceptors. The absorption coefficients of the enzyme and of its subunits in various oxidation states are also presented.

Benzyl Alcohols↗
PubMed1985

Laser-flash-photolysis studies of p-cresol methylhydroxylase. Electron-transfer properties of the flavin and haem components.

p-Cresol methylhydroxylase, a heterodimer consisting of one flavoprotein subunit and one cytochrome c subunit, may be resolved into its subunits, and the holoenzyme may then be fully reconstituted from the pure subunits. In the present study we have characterized the reduction kinetics of the intact enzyme and its subunits, by using exogenous 5-deazariboflavin semiquinone radical generated in the presence of EDTA by the laser-flash-photolysis technique. Under anaerobic conditions the 5-deazariboflavin semiquinone radical reacts rapidly with the native enzyme with a rate constant approaching that of a diffusion-controlled reaction (k = 2.8 X 10(9) M-1 X s-1). Time-resolved difference spectra at pH 7.6 indicate that both flavin and haem are reduced initially by the deazariboflavin semiquinone radical, followed by an additional slower intramolecular electron transfer (k = 220 s-1) from the endogenous neutral flavin semiquinone radical to the oxidized haem moiety of the native enzyme. During the steady-state photochemical titration of the native enzyme at pH 7.6 with deazariboflavin semiquinone radical generated by light-irradiation the haem appeared to be reduced before the protein-bound flavin and was followed by the formation of the protein-bound anionic flavin radical. This result suggests that the redox potential of the haem is higher than that of the flavin, and that deprotonation of the flavin neutral radical occurred during the photochemical titration. Reduction kinetics of the flavoprotein and cytochrome subunits were also investigated by laser-flash photolysis. The protein-bound flavin of the isolated flavin subunit was reduced rapidly by the deazariboflavin semiquinone radical (k = 2.2 X 10(9) M-1 X s-1), as was the haem of the pure cytochrome c subunit (k = 3.7 X 10(9) M-1 X s-1). Flash-induced difference spectra obtained for the flavoprotein and cytochrome subunits at pH 7.6 were consistent with the formation of neutral flavin semiquinone radical and reduced haem, respectively. Investigation of the kinetic properties of the neutral flavin semiquinone radical of the flavoprotein subunit at pH 7.6 and at longer times (up to 5s) were consistent with a slow first-order deprotonation reaction (k = 1 s-1) of the neutral radical to its anionic form.

Cytochrome c Group↗
PubMed1984

Stereochemistry of 1-(4'-hydroxyphenyl)ethanol produced by hydroxylation of 4-ethylphenol by p-cresol methylhydroxylase.

Enzymic hydroxylation of 4-ethylphenol by (a) Pseudomonas putida and (b) highly purified p-cresol methylhydroxylase gave optically active 1-(4'-hydroxyphenyl)-ethanol. The products were transformed into the phenolic methyl ethers and shown to contain 69.5% and 65.6%, respectively, of the (S)-(-)-isomer. The stereochemistry of the reaction is discussed in terms of three distinct steps occurring at the active site of the enzyme.

Ethanol↗
PubMed1981

8 alpha-(O-Tyrosyl)flavin adenine dinucleotide, the prosthetic group of bacterial p-cresol methylhydroxylase.

8 alpha-(O-Tyrosyl)riboflavin has been synthesized by condensation of the copper complex of L-tyrosine with 8 alpha-bromotetraacetylriboflavin. The structure of this synthetic product was proven by absorption and 1H NMR spectroscopy and by chemical degradation, which yielded 1 mol of tyrosine per mol of flavin. The synthetic compound comigrated wtih the (aminoacyl)riboflavin isolated from the p-cresol methylhydroxylase of Pseudomonas putida, and both showed identical absorption and fluorescence spectral properties. 8 alpha-(O-Tyrosyl)riboflavin as well as the flavin-containing decapeptide from p-cresol methylhydroxylase undergoes reductive cleavage to form riboflavin and FAD, respectively, on anaerobic treatment with dithionite. In contrast, the native enzyme, on reduction with dithionite, yields a reduced flavin via a red (anionic) flavosemiquinone intermediate, which remains covalently bound to the protein even under denaturing conditions. 8 alpha-(O-Tyrosyl)riboflavin bound to apoflavodoxin is also not cleaved on reduction with dithionite, but, instead, a blue (neutral) semiquinone of tyrosylriboflavin is generated, which is resistant to further reduction with dithionite. Three p-cresol methylhydroxylases, isolated from different strains of Pseudomonas putida, differing in molecular weight and Km values for substrates, contain the same peptide at the flavin site. These data provide definitive proof for the existence of 8 alpha-(O-tyrosyl)riboflavin in nature.

Cresols↗
PubMed1980

Chemical synthesis and some properties of 6-substituted flavins.

A number of derivatives of riboflavin and of 3-methyllumiflavin substituted in the 6 position have been synthesized starting with 6-nitro flavins, reduction to the 6-amino flavin, and diazotization, followed by reaction with the appropriate nucleophile. The absorption spectra, oxidation-reduction potentials, and the electron spin resonance spectra of the radical cationic forms of several of these synthetic compounds have been determined, including 6-S-cysteinyl-3-methyllumiflavin and 6-S-cysteinylriboflavin. The latter has been shown to be identical with the dephosphorylated form of the aminoacyl flavin isolated from trimethylamine dehydrogenase [Steenkamp, D. J., Kenney, W. C. & Singer, T. P. (1978) J. Biol. Chem. 253, 2812-2817; Steenkamp, D. J., McIntire, W., & Kenney, W. C. (1978) J. Biol. Chem. 253, 2818-2824] in regard to absorption specturm, photochemical properties, and mobility in high-voltage electrophoresis and in thin-layer chromatography. An unusually pronounced interaction between the amino group and the isoalloxazine ring system was deduced from the absorption spectra of 6-amino-3-methyllumiflavin and 6-aminoriboflavin.

Electron Spin Resonance Spectroscopy↗
PubMed1975

The Middleton outbreak: 125 cases of foodborne salmonellosis resulting from cross-contaminated food items served at a picnic and a smorgasbord.

One hundred and twenty-five of 173 people who ate at a picnic and/or a smorgasbord prepared by a bar-restaurant in a Midwestern town in September 1973 developed diarrhea, abdominal cramps, and other symptoms 23 hours (median time) later. Eleven were hospitalized. Stool cultures from 18 ill individuals grew Salmonella infantis, Salmonella agona, and Salmonella schwarzengrund. Stool cultures from 5 of 8 restaurant employees grew S. infantis or S. agona. Cultures of remaining foods and food-contact surfaces were negative. Food-specific attack rates, based on interviews with 121 eaters, implicated potato salad and chicken dressing as vehicles of transmission, both likely contaminated when prepared in pans that shortly before contained uncooked, chicken pieces suspected to have harbored salmonellae. Chickens were eventually traced to 3 farms where feed samples were found to contain Salmonella typhimurium and Salmonella cubana, raising the possibility that other feed samples may have contained the serotypes responsible for the outbreak. The main control measure was temporarily closing the food service, which was to have catered a large church picnic the next day. The outbreak had an economic impact estimated at $28,733.

Adult↗