Photosystem I Reaction Center from Cyanobacterium Green Alga and Highr Plants

Abstract

Photosystem I reaction center isolated from the thermophilic cyanobacterium Mastigocladus laminosus was found to resemble that of green algae, which also contains four different subunits. The molecular weight, P ₇₀₀ content and appearance on sodium dodecyl sulfate gels of subunits I of photosystem I reaction center from higher plants, green algae and cyanobacterium were found to be similar. Subunit I of photosystem I reaction center from these three different sources shows immunological cross reactivity. This is also true for subunit II of photosystem I reaction center which is known to be a product of the cytoplasmic translation system in green alga and higher plants.

The protein composition of leaves was followed during greening of dark grown plants, using specific antibodies raised against the individual subunits of some of the chloroplast protein complexes. Peptides that are not directly involved in a photobiochemical reaction were found to be present in etiolated leaves and their amount did not change significantly during the greening process. On the other hand, the synthesis of the different subunits of photosystem I reaction center was found to be light induced. Subunit II of the complex is the first to be synthesized in the light, and the synthesis of the other subunits then follows sequentially. Subunit I of photosystem I reaction center was found to be present in etiolated leaves and its amount was only slightly increased during the first few hours of greening.