Involvement of thiol groups in blue-light-induced phosphorylation of a plasma membrane-associated protein from coleoptile tips of Zea mays L.

Light-induced phosphorylation of a 114 kDa protein in plasma membranes isolated from the tips of maize coleoptiles was investigated in the presence of several thiol reagents at the concentration of 1 mM. Dark phosphorylation of the protein was not affected but light-induced phosphorylation was inhibited 50% with iodoacetamide, 75% with N-ethylmaleimide and 93% with N-phenylmaleimide. Previous incubation of the inhibitors with mercaptoethanol abolished the inhibitory activity completely. N-phenyl-maleimide showed the same inhibition whether it was applied before or after irradiation of the sample. Involvement of thiol group(s) in processes after photoexcitation is discussed.