Azido [14C] Atrazine Photoaffinity Technique Labels a 34-kDa Protein in Scenedesmus which Functions on the Oxidizing Side of Photosystem II

We have used azido[¹⁴C]atrazine to photoaffinity label thylakoids from wild-type (WT) Scenedesmus and a mutant, LF-1, which is blocked on the oxidizing side of photosystem II (PS II). One protein is labeled in each case, at 34 kDa in the WT and 36 kDa in LF-1. Previous comparison of the WT with LF-1 had been used to assign a PS II donor side function to the 34-kDa protein. These results suggest that this photoaffinity technique does not label the herbicide-binding protein involved in electron transfer on the reducing side of PS II.