Radiation inactivation analysis of thylakoid protein kinase systems in light and in darkness.

摘要

Chloroplast thylakoid contains several membrane-bound protein kinases that phosphorylate thylakoid polypeptides for the regulation of photosynthesis. Thylakoid protein phosphorylation is activated when the plastoquinone pool is reduced either by light-dependent electron flow through photosystem 2 (PS2) or by adding exogenous reductants, such as durohydroquinone, in the dark. The major phosphorylated proteins on thylakoid are components of light harvesting complex 2 (LHC2) and a PS2-associated 9-kDa phosphoprotein. Radiation inactivation technique was employed to determine the functional masses of various kinases for protein phosphorylation in thylakoids in spinach. Under photosynthetically active radiation (PAR), the apparent functional masses of thylakoid protein kinase systems (TPKXs) for catalysing phosphorylation of LHC2 27 and 25-kDa polypeptides were 540+or-50 and 454+or-35 kDa (448+or-23 kDa for PS2 9-kDa protein phosphorylation). The functional sizes of dark-regulated TPKXs for 25- and 9-kDa proteins were 318+or-25 and 160+or-8 kDa. The 9-kDa protein phosphorylation was independent of LHC2 polypeptides phosphorylation with regard to its TPKX functional mass. Target size analysis of protein phosphorylation indicated that thylakoid contains a group of distinct protein kinase systems. A working model is proposed to interpret the interaction between these protein kinase systems..