title: Subunit interactions change the heme active-site geometry in p-cresol methylhydroxylase.
abstract: The enzyme p-cresol methylhydroxylase [4-cresol: (acceptor) oxidoreductase (methyl-hydroxylating), EC 1.17.99.1] contains two subunits: a cytochrome c (electron transfer) subunit (cytochrome cpc) and a flavin (catalytic) subunit. When these subunits are separated by isoelectric focusing, a stable cytochrome subunit is obtained. Significant differences are observed between the one-dimensional NMR spectra of oxidized cytochrome cpc and of oxidized p-cresol methylhydroxylase. Analysis of the two-dimensional nuclear Overhauser enhancement and exchange spectroscopy (NOESY) spectrum of reduced cytochrome cpc suggests that the axial ligand, Met-50, of the stable subunit reorients by a rotation about the C gamma-S delta bond when cytochrome cpc binds to the flavin subunit. This reorientation must result in a change in bonding at the heme, which is reflected both in the para-magnetically shifted resonances and in the redox potential. p-Cresol methylhydroxylase thereby provides an interesting example of the coupling of subunit interactions to active-site structure and reactivity.
authors.affiliation: Department of Chemistry, University of Rochester, NY 14627.
authors.forename: G L
authors.initials: GL
authors.lastname: McLendon
authors.forename: S
authors.initials: S
authors.lastname: Bagby
authors.forename: J A
authors.initials: JA
authors.lastname: Charman
authors.forename: P C
authors.initials: PC
authors.lastname: Driscoll
authors.forename: W S
authors.initials: WS
authors.lastname: McIntire
authors.forename: F S
authors.initials: FS
authors.lastname: Mathews
authors.forename: H A
authors.initials: HA
authors.lastname: Hill
mesh_terms: D000494:Allosteric Regulation; D001665:Binding Sites; D003580:Cytochromes / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D006899:Mixed Function Oxygenases / Q000737:chemistry*; D011487:Protein Conformation; D016958:Pseudomonas putida / Q000201:enzymology
chemical_list: D003580:Cytochromes; D006418:Heme; D006899:Mixed Function Oxygenases; C049502:4-cresol dehydrogenase (hydroxylating)