Picosecond geminate recombination of CO to the complexes calmodulin * heme-CO and calmodulin * heme-CO * melittin

Picosecond CO recombination kinetics have been measured after photodissociation of the artificial complexes calmodulin * heme-CO and calmodulin * heme-CO * melittin. These systems show an enhancement of the geminate fraction of kinetics relative to unbound heme-CO, due in part to fast geminate kinetics (τ = 50 ps for the initial phase), as well as a decrease in the rate of migration of CO away from the binding site. This indicates that calmodulin provides a complete pocket around the heme group. Rather than competing with the hemes for binding to calmodulin, the melittin seems to act as a cap to further enclose the hemes; melittin increases the affinity of calmodulin for heme-CO, but only weakly affects the CO recombination kinetics.