KINETICS OF BINDING PROCESSES OF CYTOCHROME-C ONTO LIPOSOME SURFACES

Association processes of cytochrome C (from horse heart) onto surfaces of liposomes which were composed of L-alpha-dimyristoylphosphatidylgl ycerol and L-alpha-dimyristoylphosphatidylcholine were investigated by the stopped-flow technique. The association processes were divided in to two relaxation processes: the faster process whose apparent rate co nstant monotonously increased with the concentration of cytochrome C, and the slower process whose rate constant showed a saturation behavio r. When the number of binding sites on the liposome surface was taken into account (N = 1870), the corrected association rate constant of th e faster process (k(corr.) = 1.7 X 10(9) M(-1)s(-1)) was 2.8% of the t heoretical value (k(theor.) = 6.0 X 10(10) M(-1)s(-1)) for a binary co llision, probably due to a disadvantageous surface-searching and dehyd ration processes on the liposome and protein surfaces. The effects of deformability of liposomes, components in the lipid bilayers, and oxid ation state of cytochrome C on the rate constants for faster and slowe r steps were examined. The temperature effects on the rate constants w ere also discussed. (C) 1995 Academic Press, Inc.