Ligand binding subsequent to NO photolyses of partially unfolded cytochrome c
Article
Mikšovská, J, Larsen, RW. (2004). Ligand binding subsequent to NO photolyses of partially unfolded cytochrome c
. JOURNAL OF THE CHINESE CHEMICAL SOCIETY, 51(5 B), 1127-1132. 10.1002/jccs.200400167
Mikšovská, J, Larsen, RW. (2004). Ligand binding subsequent to NO photolyses of partially unfolded cytochrome c
. JOURNAL OF THE CHINESE CHEMICAL SOCIETY, 51(5 B), 1127-1132. 10.1002/jccs.200400167
Here we report folding studies of horse heart ferricytochrome c in the presence of NO (NO-cyt c). The midpoint concentration of guanidine hydrochloride (GuHCl) for unfolding was measured to be 2.8 M in the presence of NO and is only moderately altered relative to native cyt c under similar conditions (i.e., 2.6 M GuHCl). Recombination of NO to cyt c in the presence of 2.8 M GuHCl subsequent to photolysis is biphasic with rate constants of (4.24 ± 0.15) × 103 s-1 and 197.7 ± 3.3 s-1 with the fast and slow phase representing ∼60% and 40% relative amplitudes, respectively. NO rebinding to unfolded cyt c (in the presence of 4 M GuHCl) exhibits two phases with rate constants similar to those observed in the presence of 2.8 M GuHCl with the relative amplitude of the fast phase increasing to roughly 90%. These data suggest that NO rebinds to two populations of cyt c with one population containing a five coordinate heme and the other having a six-coordinate heme with bis-His axial ligation. These results suggest that the mis-ligated bis-His conformation forms rapidly during the refolding of cyt. c3+, although a population exists that can refold down a native pathway.
