Preparation and characterization of singly labeled ruthenium polypyridine cytochrome c derivatives

A novel two-step procedure has been developed to prepare cytochrome c derivatives labeled at specific lysine amino groups with ruthenium bis(bipyridine) dicarboxybipyridine [RuII(bpy)2(dcbpy)]. In the first step, cytochrome c was treated with the mono-N-hydroxysuccinimide ester of 4,4'-dicarboxy-2,2'-bipyridine (dcbpy) to convert positively charged lysine amino groups to negatively charged dcbpy-lysine groups. Singly labeled dcbpy-cytochrome c derivatives were then separated and purified by ion-exchange chromatography. In the second step, the individual dcbpy-cytochrome c derivatives were treated with RuII(bpy)2CO3 to form singly labeled RuII(bpy)2(dcbpy-cytochrome c) derivatives. The specific lysine labeled in each derivative was determined by reverse-phase chromatography of a tryptic digest. All of the derivatives had a strong luminescence emission centered at 662 nm, but the luminescence decay rates were increased relative to that of a non-heme protein control, RuII(bpy)2(dcbpy-lysozyme), which was 1.8 X 10(6) s-1. The luminescence decay rates were found to be 21, 16, 7.2, 5.7, 4.3, 4.3, and 3.5 X 10(6) s-1 for derivatives singly labeled at lysines 13, 72, 25, 7, 39, 86, and 87, respectively. There was an inverse relationship between the luminescence decay rates and the distances between the ruthenium labels and the heme group. The increased luminescence decay rates observed in the cytochrome c derivatives might be due to electron transfer from the excited triplet state of ruthenium to the ferric heme group. However, it is also possible that an energy-transfer mechanism might contribute to the luminescence quenching.(ABSTRACT TRUNCATED AT 250 WORDS)