Isolation and characterization of Photosystem II complexes which lack light-harvesting chlorophyll a/b proteins but retain three extrinsic proteins related to oxygen evolution from spinach

Oxygen-evolving Photosystem II (PS II) complexes, which were largely deprived of major light-harvesting chlorophyll a/b proteins (LHC II) but still associated with the 33 kDa, 23 kDa and 17 kDa extrinsic proteins related to oxygen evolution, were isolated from spinach oxygen-evolving PS II membranes with a non-ionic detergent, n-heptyl thioglucoside. A minor antenna chlorophyll-protein (CP 29) was present but in reducted amounts. The complexes contained all the constituent subunits of PS II reaction center core complexes, the 47 kDa and 43 kDa chlorophyll-carrying proteins, the D1 and D2 proteins and cytochrome b-559. In addition, three hydrophobic proteins of 29 kDa (CP 29 apoprotein), 20 kDa and 10 kDa were present. The antenna size was 80 chlorophyll a per Q_A, or 76 chlorophyll a per 4 Mn, and the complexes contained about 1 Ca²⁺ per PS II. With phenyl- or dichloro-p-benzoquinone as electron acceptor, the complexes showed high rates of oxygen evolution in the absence of exogenously added Ca²⁺. The activity became, however, strongly Ca²⁺-dependent when the 23 kDa and 17 kDa proteins, but not the bound Ca²⁺, had been removed with 1.5 M NaCl. The Ca²⁺ requirement disappeared on reconstitution of the complexes with the two proteins. The complexes were compared with other oxygen-evolving preparations having different polypeptide compositions and functions of several subunit proteins and Ca²⁺ in PS II electron transport are discussed.