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On the Role of Heme in the Formation of the Structure of Cytochrome c

1973; Elsevier BV; Volume: 248; Issue: 9 Linguagem: Inglês

10.1016/s0021-9258(19)44026-x

1083-351X

Waldo R. Fisher, Hiroshi Taniuchi, Christian B. Anfinsen,

Mass Spectrometry Techniques and Applications

In order to assess the effect of the covalently bonded heme on the stabilization of the conformation of horse heart cytochrome c, both the heme-free apo-cytochrome c and the ironfree, porphyrin-cytochrome c were prepared.The properties of these derivatives in solution were compared with those of native cytochrome c by the study of their viscosity, circular dichroism, and fluorescence.Porphyrin-cytochrome c appears to have a compact structure similar to native cytochrome c, although it is less stable to heat denaturation.It appears that the coordination of the iron atom of the heme with histidine-18 and methionine-80 results in an increase in the stability of this protein, but is not required for the folding of porphyrin-cytochrome c into a compact conformation.Apo-cytochrome c has the properties of a disordered structure.However, apo-cytochrome c can bind with the disordered heme-containing fragment of residues 1 to 65, prepared by the method of Corradin and Harbury ((1970) Biochim.Biophys.Acfa 221, 489), and forms a product with spectral properties closely resembling native cytochrome c in the same manner as does the COOH-terminal fragment of residues 66 to 104 (CORRADIN, G., AND HARBURY, H. A. (1971) Proc.Nat.Acad.Sci.U. S. A. 68, 3036).The observations indicate that the presence of the porphyrin ring covalently bonded with cysteines 14 and 17 is essential for cytochrome c to exist in the stable native conformation.