PICOSECOND GEMINATE RECOMBINATION OF CO TO THE COMPLEXES CALMODULIN-ASTERISK HEME-CO AND CALMODULIN-ASTERISK HEME-CO-ASTERISK MELITTIN

Picosecond CO recombination kinetics have been measured after photodis sociation of the artificial complexes calmodulinheme-CO and calmoduli nheme-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 (tau = 50 ps for the initial phase), as well as a d ecrease in the rate of migration of CO away from the binding site. Thi s 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; mel ittin increases the affinity of calmodulin for heme-CO, but only weakl y affects the CO recombination kinetics.