The effect of diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), trifluoperazine and lauroylcholinechloride on P-680 + reduction and oxygen evolution

Abstract

Comparative measurements of flash-induced oxygen yield and P-680 + reduction kinetics were carried out under repetitive flash excitation of Photosystem II (PS II) particles. In control samples with intact oxygen evolution capacity, 67% of P-680 + was reduced in the nanosecond time-scale. Upon modification of PS II particle preparations with the inhibitors diisothiocyanostilbene-2,2′-disulfonic acid, trifluoperazine or lauroylcholinechloride, a state in Photosystem II is achieved in as much as 50% of the centers in which the normal nanosecond component in the P-680 + reduction kinetics remains intact for at least 128 actinic flashes without giving rise to a detectable contribution to O 2 evolution. Arguments are presented to show that under these special inhibitory conditions, the rapid transfer of electrons from the primary electron donor, Z, to P-680 + is not mediated by a normal ADRY-type mechanism nor through electron donation by the compounds themselves. The results imply that the site of inhibition of these compounds is near the O 2 release site in the water-splitting enzyme and that the amplitude of the nanosecond component of the P-680 + reduction kinetics does not necessarily correlate with oxygen-evolution capacity even under repetitive flash-excitation conditions.