A temperature-jump study of the electron transfer reactions in Hansenula anomala flavocytochrome b sub(2)

Temperature-jump experiments on flavocytochrome b sub(2) were carried out at different levels of heme reduction at pH 7.0 and 6.0, and as a function of pyruvate concentration. The relaxation, corresponding to an increase in the concentration of reduced heme, is in no case a simple process. At pH 7.0 the mean reciprocal relaxation times is 1/ tau * = 190s super(-1), independent of enzyme concentration, wavelength of observations and percentage of heme reduction. Flavin semiquinone has been identified as the major electron donor to the heme in this process. At the same pH the presence of pyruvate in the millimolar concentration range increases the relaxation rate and affects its amplitude. The latter effect could be accounted for by a change in redox equilibria between heme and flavin upon pyruvate binding.