A FLAVOPROTEIN MAY MEDIATE THE BLUE LIGHT‐ACTIVATED BINDING OF GUANOSINE 5'‐TRIPHOSPHATE TO ISOLATED PLASMA MEMBRANES OFPisum sativumL.*

Abstract

Abstract—A blue light photoreceptor has not been identified in higher plants. Most proposals for a blue light‐absorbing chromophore lack evidence for a direct connection between the putative chromophdre and a biological effect. Fluorescence data for the plasma membrane from etiolated buds ofPisum sativumL. suggest that we are measuring fluorescence emission of flavin species, and probably not pterin species. Fluorescence data indicate that a putative flavin exists associated with a protein or protein complex in the plasma membrane. Excitation of plasma membranes that were boiled in the presence of 0.1% sodium dodecyl sulfate and treated with blue light yields a fluorescence band with a maximum of approximately 552 nm. This fluorescence emission can be rapidly quenched by the flavin antagonists phenylacetic acid (PAA) and KI. Blue light‐enhanced binding of guanosine 5'‐[Γ‐thio]triphosphate (GTPγS) to a protein in the plasma membrane is strongly inhibited by PAA, KI, and NaN3, all quenchers of flavin excited states, indicating that a chromophore for this photoreaction may be a flavin associated with a plasma membrane protein. The above evidence is consistent with the participation of a flavin as the chromophore for the light‐induced GTP‐binding reaction in pea plasma membrane.