Chlorophyll-proteins of two photosystem I preparations from maize

Abstract

Two photosystem I (PSI) preparations were purified by non-denaturing SDS-PAGE or sucrose gradient ultracentrifugation and examined as to their chlorophyll-protein composition. In both preparations a minimum of two chlorophyll-proteins can be distinguished in addition to the 110 kDP-700 Chla-P1 complex. One (LHCI-730) is a chlorophyll-protein (Mr 40 kD) having a high chlorophylla/b ratio, and a major 77 K fluorescence peak at 730 nm. It consists of three polypeptides with apparent molecular weights of 21, 22.5 and 24 kD. Another chlorophyll-protein (LHCI-680) with a lower molecular weight (Mr 25 kD) fluoresces at 77 K with a maximum at 680 nm. This chlorophyll-protein has a high chlorophyllb content and two constituent polypeptides of 20 and 25 kD. Absorption, 77 K fluorescence and circular dichroism spectra of the PSI related chlorophyll-proteins are presented and compared with those of photosystem II chlorophyll-proteins from maize thylakoids. We propose a model for energy transfer in the photosystem I reaction centre with the following sequence: LHCI-730→LHCI-680 →Chla-P1. LHCI-680 acts as a connecting antenna which can also transfer energy from Chla/b-P2. This model was used to interpret the 77 K fluorescence emission from two barley mutants.