W. Oettmeier et al., ON THE ORIENTATION OF PHOTOSYSTEM-II INHIBITORS IN THE Q(B)-BINDING NICHE - ACRIDONES, XANTHONES AND QUINONES, Zeitschrift fur Naturforschung. C, A journal of biosciences, 48(3-4), 1993, pp. 146-151
The orientation of acridones, xanthones, 1,4-benzo- and naphthoquinone
s within the photosystem II Q(B) herbicide-binding niche was studied b
y means of mild trypsination and by estimation of pI50-values in Chlam
ydomonas reinhardtii D1 mutants (Val219 > Ile, Ala251 > Val, Phe255 >
Tyr, Ser264 > Ala, Asn266 > Thr, and Leu275 > Phe). As judged from the
R/S-values (ratios of I50-values resistant versus susceptible type) c
lose to 1 in all mutants, the acridones and xanthones do not have stro
ng interactions with the parent amino acids. Contrary, the quinones ex
hibit extreme low R/S-values down to 0.003 (for 2,5-dibromo-3-methyl-6
-isopropyl-1,4-benzoquinone; DBMIB) in the Ser264 mutant. This extreme
negative cross resistance or supersensitivity indicates that the quin
ones do not form a hydrogen bond to the serine hydroxyl group.