Formation of cross-linked complex of photosynthetic reaction center and horse heart cytochrome c: an approach for molecular organization with cross-linkage

A new type of cross-linked complex was created between a photosynthetic reaction center (RC) from Rhodobacter sphaeroides R-26 and cytochrome c (cyt c) from horse heart. The heterobifunctional reagent, N-succinimidyl 3-(2-pyridyldithio) propionate, was used for the cross-linkage. The complex was purified to obtain those that had cyt c linked to the H subunit of the RC. The molar ratio of cyt c to RC in the complex was 1.5:1. Mid-point potential of cyt c in the complex shifted slightly by − 20 mV but that of bacteriochrorophyll dimer ((Bchl)2) remained unchanged. The rate of the charge recombination of (Bchl)2 was in good agreement with native RC. However, the electron transfer from cyt c to RC was depressed in the complex owing to the insufficient contact between cyt c and the cytochrome-binding site of the RC.