The oxygen‐evolving photosystem II core complex

Abstract

Digitonin extracts of spinach thylakoid membranes obtained as 100000 × g supernatant have been shown to retain part of the oxygen‐evolving activity if the extraction is carried out at acidic pH. The photosystem II reaction center complex with a uniform particle size of 300–500 kDa was purified from the extracts by ion‐exchange/gel‐permeation chromatography performed at pH 6.0 using DEAE‐Toyopearl‐650. The purified materials contained only two polypeptides of about 22 (not 24) and 33 kDa, in addition to those of the reaction center core complex, i.e., 47, 43, 30 and 10 kDa. The purified complex was fairly active in the photochemical oxygen evolution supported by phenyl‐ p ‐benzoquinone (~150μmol oxygen evolved·mg chl −1 ·h −1 ) and DCIP photoreduction with water. From these results it is concluded that the principal site of water oxidation is associated rather with the photosystem II core complex than with the water soluble peripheral complex consisting of 18,24 and 33 kDa polypeptides and that the thylakoid membrane structure is not essential for manifestation of oxygen‐evolving activity.