Association of iron-protoporphyrin-IX (hemin) with myosins

Addition of myosins isolated from guinea pig heart and rabbit skeletal muscle to hemin solutions resulted in the appearance of new absorption spectra indicating association of hemin and the myosins. Binding stoichiometry based on absorption changes was found to be two hemin sites per myosin molecule. The binding constants calculated from quenching of the intrinsic fluorescence of the myosins by hemin are Ka = 7 (+/- 2) 10(6) M-1 for skeletal muscle myosin, and Ka = 3 (+/- 1) x 10(7) M-1 for heart muscle myosin. Based on these findings, myosins are suggested as potential transporters of free hemin between cell organelles.