Charge interactions of cytochrome c with cytochrome c oxidase

The pyridoxal phosphate (PLP) modification of the lysine amino groups in cytochrome c causes decrease in the reaction rate with cytochrome c oxidase. The rate constants for (PLP)2-cyt. c, PLP(Lys 86)-cyt. c, PLP(Lys 79)-cyt. c and native cytochrome c (at pH 7.4, I = 0.02) are 3.6 X 10(-3) sec-1, 5.5 X 10(-3) sec-1, 5.2 X 10(-3) sec-1 and 9.8 X 10(-3) sec-1, respectively. In spite of the same positive charge of singly PLP-cytochromes c the reaction between PLP(Lys 86)-cyt. c and cyt. c oxidase exhibits the ionic strength dependence that differs from those of the PLP(Lys 79)-cyt. c. The rate constants at zero and infinite ionic strength for PLP(Lys 86)-cyt. c is 2-fold less than that for PLP(Lys 79)-cyt. c. The positively charged cytochrome c lysines 86 and 79 form two from four or five predicted complementary charge interactions with carboxyl groups on cytochrome c oxidase.