Abstract
PsbO1 is exclusively nitrated when isolated thylakoid membranes are incubated in a buffer bubbled with nitrogen dioxide (NO(2)) containing NO(2) and nitrite. NO(2) is the primary intermediate for this selective nitration. Isolated thylakoid membranes were incubated in NO(2)-bubbled buffer at 25°C in the light or dark. Protein analysis confirmed the selective nitration of PsbO1. Illumination was found to be essential in PsbO1 nitration. A nitration mechanism whereby nitratable tyrosine residues of PsbO1 are, prior to nitration, selectively photo-oxidized by photosynthetic electron transport to tyrosyl radicals to combine with NO(2) to form 3-nitrotyrosine was hypothesized. We tested the electron transport inhibitors 3-(3,4-dichlorophenyl)-1,1- dimethylurea, sodium azide, and 1,5-diphenylcarbazide and found distinct inhibition of nitration of PsbO1. We also propose a possible nitration mechanism.