Journal article
15N and1H NMR Studies of Rhodospirillum rubrum Cytochrome c2
Biochemistry (Easton), Vol.27(6), pp.1949-1956
03/22/1988
DOI: 10.1021/bi00406a022
PMID: 2837275
Abstract
15N-enrichedcytochrome c2was purified from Rhodospirillum rubrum that had been grown on15NH4C1, and the diamagnetic iron(II) form of the cytochrome was studied by15N andlH NMR spectroscopy.15N resonances of the four pyrrole nitrogens, the ligand histidine nitrogens, the highly conserved tryptophan indole nitrogen, and some proline nitrogens are assigned. The resonances of the single nonligand histidine are observed only at low pH because of severe broadening produced by proton tautomerization. The resonances of exchangeable protons bonded to the nitrogens of the ligand histidine, the tryptophan, and some amide groups are also assigned. The exchange rates of the nitrogen-bound protons vary greatly: most have half-lives of less than minutes, the indolic NH of Trp-62 exchanges with a half-time of weeks, and the ligand histidine NH proton exchanges with a half-time of months. The latter observation is indicative of extreme exclusion of solvent from the area surrounding the ligand histidine and lends credence to theories implicating the degree of hydrophobicity in this region as an important factor in adjusting the midpoint potential. The dependence of the15N and1H NMR spectra of ferrocytochrome c2on pH indicates neither the Trp-62 nor the ligand His side chains become deprotonated to any appreciable extent below pH 9.5. The His-18 NH remains hydrogen bonded, presumably to the Pro-19 carboxyl group, throughout the pH titrations. Because neither deprotonated nor non-hydrogen-bonded forms of His-18 are observed in spectra of the ferrocytochrome, the participation of such forms in producing a heterogeneous population having different g tensor values seems unlikely. A single ionization, occurring with a pK of 6.8, causes the resonances of the pyrrole nitrogens and several groups near the heme to shift. This ionization, attributed to the protonation/deprotonation of His-42 or a His-42-heme propionate hydrogen-bonded pair, appears to affect a wide range of groups near the heme, perhaps by altering the packing of the Ω loops which cover that region of the protein
Details
- Title: Subtitle
- 15N and1H NMR Studies of Rhodospirillum rubrum Cytochrome c2
- Creators
- Liping P YuGary M Smith
- Resource Type
- Journal article
- Publication Details
- Biochemistry (Easton), Vol.27(6), pp.1949-1956
- Publisher
- Amer Chemical Soc
- DOI
- 10.1021/bi00406a022
- PMID
- 2837275
- ISSN
- 0006-2960
- eISSN
- 1520-4995
- Number of pages
- 8
- Grant note
- R01GM034194 / NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA; NIH National Institute of General Medical Sciences (NIGMS) GM-34194 / NIGMS NIH HHS; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA; NIH National Institute of General Medical Sciences (NIGMS)
- Language
- English
- Date published
- 03/22/1988
- Academic Unit
- Biochemistry and Molecular Biology; Medicine Administration
- Record Identifier
- 9984627343502771
Metrics
12 Record Views