[Show abstract][Hide abstract] ABSTRACT: PSI-G is a subunit of photosystem I in eukaryotes. The function of PSI-G was characterized inArabidopsis plants transformed with a psaGcDNA in antisense orientation. Several plants with significantly decreased PSI-G protein content were identified. Plants with
reduced PSI-G content were indistinguishable from wild type when grown under optimal conditions, despite a 40% reduction of
photosystem I. This decrease of photosystem I was correlated with a similar reduction in state transitions. Surprisingly,
the reduced photosystem I content was compensated for by a more effective photosystem I because the light-dependent reduction
of NADP+ in vitro was 48% higher. Photosystem I antenna size determined from flash-induced P700 absorption changes did not reveal any significant
effect on the size of the photosystem I antenna in the absence of PSI-G, whereas a 17% reduction was seen in the absence of
PSI-K. However, nondenaturing green gels revealed that the interaction between photosystem I and the light-harvesting complex
I was less stable in the absence of PSI-G. Thus, PSI-G plays a role in stabilizing the binding of the peripheral antenna.
The increased activity in the absence of PSI-G suggests that PSI-G could have an important role in regulation of photosystem
Preview · Article · Feb 2002 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: The light-harvesting antenna of barley photosystem I (LHCI) was isolated from native photosystem I (PSI) complexes and fractionated into three pigment-protein subcomplexes using two consecutive rounds of green gel electrophoresis. Each complex showed a characteristic polypeptide composition and low-temperature fluorescence emission spectrum; they were designated as LHCI-730, LHCI-680A and LHCI-680B. Their four apoproteins of 21, 22, 23 and 25 kDa were purified and NH2-terminal sequences were determined; in the case of the NH2-terminally blocked 25-kDa protein, an internal sequence was obtained after cleavage with endoproteinase Lys-C. This made possible an assignment of the four proteins to the four types (I-IV) of genes coding for chlorophyll a/b proteins of PSI (cab or lha genes). The LHCI-730 complex was isolated as a heterodimer composed of the 21-kDa (LHCI type IV) and the 22-kDa (LHCI type I) polypeptides. Each LHCI-680 complex had a single apoprotein. LHCI-680A consisted of the 25-kDa (LHCI type III) and LHCI-680B of the 23-kDa (LHCI type II) polypeptides. LHCI-680B was associated with the non-pigmented PSI-E subunit, indicating that this protein may function in the binding of this antenna to the reaction centre.
Preview · Article · Jun 1992 · European Journal of Biochemistry