HETEROGENEITY IN PHOTOSYSTEM-II-ALPHA - EVIDENCE FROM FLUORESCENCE AND GEL-ELECTROPHORESIS EXPERIMENTS

The antenna size of different thylakoid membrane vesicles originating from grana partitions and enriched in PS IIα was determined by measuring the kinetics of the variable fluorescence and by gel electrophoresis of pigment-protein complexes. Inside-out thylakoid vesicles were fractionated by sonication and phase partition and separated into different subpopulations of PS IIα vesicles. The kinetics of the rise in the variable fluorescence of these subpopulations differed, demonstrating a heterogeneity in functional antenna size among the PS IIα. Analysis by gel electrophoresis showed that the fractions which have a more rapid rise in variable fluorescence, and hence a larger functional antenna size, also had a larger ratio of LHCII/PS II core polypeptides. The relative content of the 25 kDa polypeptide of LHCII increased with antenna size. There is thus a heterogeneity both with respect to the quantitative and the qualitative composition of the antenna of PS IIα. The results suggest that in vivo there are different domains in the partition region of the thylakoid membrane which have different average antenna size of PS IIα. The results lend further support to previous work in which heterogeneity of the antenna size of PS IIα of the same types of vesicles population was demonstrated by light saturation curves of oxygen evolution (Albertsson, P.-Å. and Yu S.-G. (1988) Biochim. Biophys. Acta 936, 215-221). © 1990.