PRESENCE OF THE PHOTOACTIVE REACTION-CENTER CHLOROPHYLL OF PSI (P700)IN DARK-GROWN CELLS OF A CHLOROPHYLL-DEFICIENT MUTANT OF CHLORELLA-KESSLERI

Compositions of pigments and polypeptides of pale green membranes that had been isolated from dark-grown cells of a chlorophyll-deficient mu tant of Chlorella kessleri were investigated. They contained Chi a in a level corresponding to about 1% of that present in the thylakoid mem branes isolated from autotrophically grown wild-type cells and a trace amount of chlorophyllide a, but neither Chi b nor carotenoids. The po lypeptide profile of the mutant membranes was similar to that of membr anes isolated from wild-type cells that were grown in the dark. Neithe r the chlorophyll-binding subunits of PSI nor the apoproteins of LHCP were detected by SDS-PAGE and immunoblot analysis. However, the light- minus-dark difference spectrum of the mutant membranes revealed the pr esence of the reaction-center chlorophyll of PSI (P700) at a molar rat io of 190 chlorophyll (Chl a plus Chlide a) per P700. P700 was more st able than Chi a and Chlide a in the light so that prolonged illuminati on led to a decline in the Chl/P700 ratio to 24. The initial rate of P 700 photooxidation in the mutant membranes was comparable to that in C P1 isolated from the dark-grown wild-type cells. Under illumination wi th strong light, the initial rate was decreased in parallel to the dec rease in Chl/P700 ratio. The results suggest that most of Chi present in the mutant membranes can transfer excitation energy to P700.