PROTEIN GLOBULE SPEEDS UP THE HEME PHOTOREDUCTION

Abstract— To answer the question whether the external electron can be transferred through the protein globule, the rate of photoreduction of the free heme with dye radicals was compared with that of the heme in various protein environments, in cytochrome c, myoglobin and in heme-HSA complex. In all cases the globular part of proteins did not prevent the photoreduction of the heme; in fact, it speeded up the process. As determined by flash-photolysis, the rate constants(1–5) x 10⁸ M^-1 s^-1 are close to that of the diffusion controlled reactions between molecules of similar size. The experimental data confirm the hypothesis that the native protein globule can transfer external unpaired electrons rather effectively. We make the supposition that this ability is a general feature of proteins but not a function related to electron carriers only.