Inhibition of electron transport in photosystem II by hydroxylamine

Biochemistry 1988, 27, 6297-6306

6297

Inhibition of Electron Transport in Photosystem I1 by NH20H: Further Evidence for Two Binding Sites? Mohanram Sivaraja and G. Charles Dismukes* Department of Chemistry, Princeton University, Princeton, New Jersey 08544 Received December 1 1 , 1987; Revised Manuscript Received April 4, 1988

ABSTRACT: The reaction of hydroxylamine, a substrate analogue of the water-oxidizing complex

(WOC),

with spinach photosystem I1 (PSII) membranes has been further studied by using EPR spectroscopy to monitor the stepwise oxidation of donors and reduction of electron acceptors during successive low-temperature illuminations [Sivaraja, M., & Dismukes, G. C. (1988) Biochemistry 27, 3467-34751. In addition to its well-known binding on the donor side of PSII, hydroxylamine binds in the dark with high affinity (KD< 10 pM;