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NMR study of the alkaline isomerization of ferricytochrome c
Author(s) -
Hong Xiaole,
Dixon Dabney White
Publication year - 1989
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(89)80262-5
Subject(s) - isomerization , chemistry , reaction rate constant , cytochrome c , proton nmr , equilibrium constant , nmr spectra database , kinetics , stereochemistry , cytochrome , medicinal chemistry , crystallography , spectral line , catalysis , organic chemistry , enzyme , biochemistry , physics , quantum mechanics , astronomy , mitochondrion
The pH‐induced isomerization of horse heart cytochrome c has been studied by 1 H NMR. We find that the transition occurring in D 2 O with a p K a measured as 9.5±0.1 is from the native species to a mixture of two basic forms which have very similar NMR spectra. The heme methyl peaks of these two forms have been assigned by 2D exchange NMR. The forward rate constant (native to alkaline cytochrome c ) has a value of 4.0±0.6 s −1 at 27°C and is independent of pH; the reverse rate constant is pH‐dependent. The activation parameters are Δ H ‡ = 12.8±0.8 kcal·mol 1 , Δ S ‡ = − 12.9±2.0 e.u. for the forward reaction and Δ H ‡ = 6.0±0.3 kcal·mol −1 , Δ S ‡ = − 35.1±1.3 e.u. for the reverse reaction (pH*=9.28). Δ H ° and Δ S ° for the isomerization are 6.7±0.6 kcal·mol −1 and 21.9±1.0 e.u., respectively.