Radioisotopic evidence for the polypeptides associated with photosystem II

Direct radioisotopic evidence for the polypeptides associated with oxygen evolution in a non-destructive approach by comparing the polypeptides of photosystem II (PS II) particles in etioplasts that lack O2 evolution with that of chloroplasts that exhibit high rates of oxygen evolution is reported. Polypeptide analysis by coomassie blue staining revealed that 32, 23 and 15 kDa proteins were absent in etioplast particles but developed in chloroplast PS II particles after illumination. However, a strikingly different picture was obtained when labelled polypeptides were analyzed from the fluorograph. While the new proteins identified by coomassie blue staining were also labelled, intensely labelled major polypeptides of molecular range 40, 41, 43 kD and minor polypeptides of molecular range 47, 48, 51 kD were observed in chloroplast PS II particles but not in etioplasts or etioplast particles; these labelled polypeptides were so prominent that they could be identified even in thylakoid membranes.