Studies on Chemically Modified Cytochrome c*

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Abstract
When bovine cytochrome c was modified with a large excess of acetic anhydride, 22-acetyl-cytochrome c was obtained in which all of lysine (18 moles) and tyrosine (4 moles) residues were acetylated. The spectral changes in the oxidized form, the autoxi-dizability and the easiness in binding with the externally added ligands such as cyanide and carbon monoxide showed that the conformation around heme in 22-acetyl-cyto-chrome c might be appreciably disturbed. The transition between the different spin states of heme iron was observed with the acetylated cytochrome c in the pH region below 7. At room temperature, it occurred at pH 5.0, and at liquid nitrogen temperature below pH1.0. It was found that the high spin state at room temperature in the pH region between 1.0 and 7.0 was converted to the low spin state at liquid nitrogen temperature, and that they made a thermally equilibrated mixture between –160°C and —70°C.

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