Characterization of pH-dependent conformational heterogeneity in Rhodospirillum rubrum cytochrome c sub 2 using sup 15 N and sup 1 H NMR

Journal Article · Tue Mar 27 00:00:00 EST 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00464a005· OSTI ID:6172489

Yu, L P; Smith, G M ^[1]

---

1. Univ. of California, Davis (USA)

The {sup 15}N-enriched ferricytochrome c{sub 2} from Rhodospirillum rubrum has been studied by {sup 15}N and {sup 1}H NMR spectroscopy as a function of pH. The {sup 15}N resonance of the heme and ligand {tau} nitrogen are broadened beyond detection because of paramagnetic relaxation. The {sup 15}N resonance of the ligand histidine {pi} nitrogen was unambiguously identified at 184 ppm (pH 5.6). The {sup 15}N resonances of the single nonligand histidine are observed only at low pH, as in the ferrocytochrome because of the severe broadening caused by tautomerization. The dependence of the {sup 15}N and {sup 1}H spectra of the ferricytochrome on pH indicated that the ligand histidine {pi} NH does not dissociate in the neutral pH range and is involved in a hydrogen bond, similar to that in the reduced state. Transitions having pK{sub a}'s of 6.2, 8.6, and 9.2 are observed in the ferricytochrome. Structural heterogeneity leads to multiple resonances of the heme ring methyl at position 8. The exchange rate between the conformations is temperature dependent. The transition with a pK{sub a} of 6.2 is assigned to the His-42 imidazole group. The displacement of the ligand methionine causes gross conformational change near the heme center. There are multiple conformations at high pH, as judged by saturation-transfer experiments. The N-terminus of the ferricytochrome has a pK{sub a} of 8.6. In contrast to its partially restricted mobility in the reduced state, it is found to be very mobile, reflecting a looser structure of the ferricytochrome.

• OSTI ID: 6172489
• Journal Information: Biochemistry; (USA), Vol. 29:12; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CYTOCHROMES
CONFORMATIONAL CHANGES
PH VALUE
BIOLOGICAL EFFECTS
RHODOSPIRILLUM
NUCLEAR MAGNETIC RESONANCE
AMMONIUM CHLORIDES
HEME
LIGANDS
NITROGEN 15
PROTONS
TEMPERATURE DEPENDENCE
AMMONIUM COMPOUNDS
AMMONIUM HALIDES
BACTERIA
BARYONS
CARBOXYLIC ACIDS
CHLORIDES
CHLORINE COMPOUNDS
ELEMENTARY PARTICLES
FERMIONS
HADRONS
HALIDES
HALOGEN COMPOUNDS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
MICROORGANISMS
NITROGEN ISOTOPES
NUCLEI
NUCLEONS
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PIGMENTS
PORPHYRINS
PROTEINS
RESONANCE
STABLE ISOTOPES
550201* - Biochemistry- Tracer Techniques