H-NMR study of temperature-induced structure alteration at the active site of horse heart cytochrome c.
The molecular structure of the active site of horse heart met-cyano cytochrome c, as a function of temperature, has been investigated using 1H-NMR. A temperature dependence study of the NMR spectra revealed that one heme methyl proton resonance exhibits anti-Curie behavior, i.e., the hyperfine shift increases with increasing temperature. Analyses of the average heme methyl proton hyperfine shift and the proximal His imidazole proton resonances indicated that the iron-His bonding interaction in this protein is essentially independent of temperature. Since such an anomalous temperature dependence of the heme methyl proton resonance disappears in met-cyano complex of a heme peptide prepared by enzymatic degradation of the protein [Smith, M. and McLendon, G. (1981) J. Am. Chem. Soc. 103, 4912-4921], the anti-Curie behavior observed for the heme methyl proton resonance in met-cyano cytochrome c is attributed to a rotational displacement of the heme about the iron-His bond relative to the protein moiety due to a temperature-dependent conformational alteration of the heme-protein linkage. Such rotational mobility of heme at the active site of a protein may be responsible for the anomalous temperature dependence of heme methyl proton hyperfine shifts reported for many c-type ferri cytochromes.
Yamamoto
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Department of Chemistry, University of Tsukuba, Ibaraki.
D000818:Animals; D001665:Binding Sites; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism*; D006418:Heme; D006639:Histidine / Q000737:chemistry; D006736:Horses; D007093:Imidazoles / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009206:Myocardium / Q000201:enzymology*; D011522:Protons; D013696:Temperature
D003574:Cytochrome c Group; D007093:Imidazoles; D011522:Protons; D006418:Heme; D006639:Histidine; C029899:imidazole