IS THERE ANY DIFFERENCE IN THE PLASTOQUINONE-PROTEIN LINK FOR Q(I) (Q(A)) AND Q(II) (Q(B)) IN PSU - AN INDO STUDY

INDO/2 studies have been carried out for the elucidation of the relati ve environment of the plastoquinones Q(I) and Q(II) in thylakoid discs in chloroplast. The corresponding quinones in bacteria are Q(A) and Q (B), which are known to be plastoquinones, menaquinones, or ubiquinone s. We show that a major part of the free energy of reduction of Q(II) by Q(I) (-0.13 eV in vivo) can be accounted for if the plastoquinone o f Q(I) contains, in lieu of one of the methyl substituents, a side cha in like -NHR or -NHCOR which serves as a link to the protein moiety in the photosynthetic unit (PSU). Here R represents an alkyl group. Chai ns like -NRR' and -NRCOR' are also possible substituents of Q(I). The remaining part of the free energy of reduction can be attributed to a slight difference in the polarizable environment not directly bonded t o the plastoquinones.