Pyridoxal phosphate modified cytochromes c. Identification and electron transfer properties.

The preparation, purification and characterization of the three singly, three doubly and one triply substituted derivatives of cytochrome c modified by pyridoxal phosphate (PLP) at lysine residues are reported. The PLP positions in PLP derivatives were determined by the amino acid analysis and sequence of PLP peptides. The results identified the lysine at position 86 in one of the singly substituted, lysine 79 in the other singly substituted and lysines 86 and 79 in the third doubly substituted cytochrome c derivatives. The area surrounding phenylalanine 82 forms the predominant PLP binding site on the cytochrome c molecule. The visible, CD and proton NMR spectra, the full intensity of the conformation-sensitive 695 nm band and the oxidation-reduction properties provide evidence to confirm the conclusion that singly and doubly substituted PLP cytochromes c retain the native conformation. The ability to restore both succinate and ascorbate/TMPD oxidation in cytochrome c-depleted mitochondria decreases in the order: native cytochrome c greater than PLP-Lys-79-cytochrome c greater than PLP-Lys-86-cytochrome c greater than PLP-Lys-79,86-cytochrome c greater than triply substituted derivative.