Blue light-induced Absorbance Changes in Membrane Fractions from Corn and Neurospora

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Abstract
Blue light-induced absorbance changes were measured from differentially centrifuged membrane fractions from dark-grown coleoptiles of Zea mays L., and mycelia from an albino mutant of N. crassa. Actinic irradiation caused changes in absorbance consistent with a flavin-mediated reduction of a b-type cytochrome. Both corn and Neurospora showed similar light-minus-dark difference spectra, dose response curves and kinetics of dark recovery after irradiation. The photoreducible cytochrome system from Neurospora showed the same distribution as the activity of a Na-stimulated ATPase, thought to be a plasma membrane marker, in differential centrifugation experiments. The fraction showing the absorbance change did not co-sediment with the mitochondria, nor with the endoplasmic reticulum. Comparison of absorption spectra of fully oxidized, partially reduced and fully reduced preparations showed that approximately a 30% reduction of the cytochromes involved with the process was needed to obtain the light-induced absorbance changes.