Reversible unfolding of cytochrome c upon interaction with cardiolipin bilayers. 2. Evidence from phosphorus-31 NMR measurements

Journal Article · Tue Apr 23 00:00:00 EDT 1991 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00230a011· OSTI ID:5398039

Spooner, P J.R.; Watts, A ^[1]

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1. Univ. of Oxford (England)

{sup 31}P NMR measurements were conducted to determine the structural and chemical environment of beef heart cardiolipin when bound to cytochrome c. {sup 31}P NMR line shapes infer that the majority of lipid remains in the bilayer state and that the average conformation of the lipid phosphate is not greatly affected by binding to the protein. An analysis of the spin-lattice (T{sub 1}) relaxation times of hydrated cardiolipin as a function of temperature describes a T{sub 1} minimum at around 25{degree}C which leads to a correlation time for the phosphates in the lipid headgroup of 0.71 ns. The relaxation behavior of the protein-lipid complex was markedly different, showing a pronounced enhancement in the phosphorus spin-lattice relaxation rate. This effect of the protein increased progressively with increasing temperature, giving no indication of a minimum in T{sub 1} up to 75{degree}C. The enhancement in lipid phosphorus T{sub 1} relaxation was observed with protein in both oxidation states, being somewhat less marked for the reduced form. The characteristics of the T{sub 1} effects and the influence of the protein on other relaxation processes determined for the lipid phosphorus (spin-spin relaxation and longitudinal relaxation in the rotating frame) point to a strong paramagnetic interaction from the protein. A comparison with the relaxation behavior of samples spinning at the magic angle was also consistent with this mechanism. The results suggest that cytochrome c reversibly denatures on complexation with cardiolipin bilayers, such that the electronic ground state prevailing in the native structure of both oxidized and reduced protein can convert to high-spin states with greater magnetic susceptibility.

• OSTI ID: 5398039
• Journal Information: Biochemistry; (United States), Vol. 30:16; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
CARDIOLIPIN
NUCLEAR MAGNETIC RESONANCE
CYTOCHROMES
ELECTRON TRANSFER
LIPIDS
MEMBRANES
PHOSPHORUS 31
RELAXATION TIME
SPIN-LATTICE RELAXATION
TEMPERATURE DEPENDENCE
ESTERS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PHOSPHOLIPIDS
PHOSPHORUS ISOTOPES
PIGMENTS
PROTEINS
RELAXATION
RESONANCE
STABLE ISOTOPES
550601* - Medicine- Unsealed Radionuclides in Diagnostics