Title

Characteristics of two atrazine-binding sites that specifically inhibit Photosystem II function

Document Type

Article

Publication Date

9-13-1991

Abstract

In pea thylakoids, [14C]atrazine is found to have two binding sites per active oxygen-evolving complex; one with high-binding affinity and one with low-binding affinity. The high affinity site has a Kd = 80 nM, is present at a concentration of 120 nM (1 site/470 Chl); binds in less than 500 ms; and blocks the electron flow reaction, Qa-Qb→QaQb-. The low affinity site has a Kd = 420 nM; is present at a concentration of 120 nM (1 site/470 Chl); binds with a half-time of 4 to 5 s; and partially inhibits the charge recombination reaction in Photosystem II, Sn+1Qa- → SnQa. In the same thylakoids, the concentration of Photosystem II centers active in oxygen evolution is 100 nM (1/540 Chl) and the concentration of those active in charge separation is 120 nM (1/450 Chl). Therefore, there are approximately two atrazine-binding sites per Photosystem II reaction center; one with high affinity and one with low affinity. High-affinity labelling with [14C]azidoatrazine is associated with a 34.5 kDa protein, which is identified as D1, using polyclonal antisera. Low-affinity labelling with [14C]azidoatrazine is associated with a 30-32 kDa protein, which is identified as D2 with the monoclonal antibody FQC3. Our findings indicate that both high-and low affinity sites are specific for Photosystem II function. © 1991 Elsevier Science Publishers B.V. All rights reserved.

Publication Source (Journal or Book title)

BBA - Bioenergetics

First Page

312

Last Page

322

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