In the mutant CC-1047 of Chlamydomonas reinhardtii, LDS-PAGE showed that the chlorophyll-protein complex I (CPI) is almost absent. The mutant could not grow in a culture medium without organic carbon source while the wild type (WT) C. reinhardtii grew quickly. When an organic carbon source was added into the culture medium, the mutant grew almost as well as WT. The rate of photosystem 1 (PS1) electron transport (DCPIP→MV) and the rate of whole chain electron transport (H2O→MV) of chloroplasts of the CC-1047 mutant were both lower than those of WT. The photophosphorylation activity, photosynthetic O2 evolution rate, and rate of NADP+ photoreduction of CC-1047 were also much lower than the activities of WT. There were some differences in ATPase activity between the mutant and WT. Two different activation ways were used to activate the latent ATPase using methanol and dithiothreitol (DTT) as activation substrate. More methanol and DTT were required for the mutant than WT to obtain the maximum activity. Thus the photosynthetic apparatus could not operate normally when CPI was absent because of the abnormal PS1 electron transport. Meanwhile, the other adjacent complexes of the thylakoid membrane, for example, ATP synthase complex, were slightly affected. and Qing-Xiu Tang, Zhang-Lin Ni, Jia-Mian Wei.
The cytosolic and chloroplastic isoforms of glucose-6-phosphate dehydrogenase (G6PDH) were separated and purified from barley leaves (Hordeum vulgare L.). In etiolated leaves, only the cytosolic isoform was expressed. The molecular mass of the cytosolic enzyme, G6PDH1, was 112±8 kDa and that of the chloroplast enzyme, G6PDH2, was 136±7 kDa. The Km values for glucose-6-phosphate and NADP were 0.133 and 0.041 mM for G6PDH1, and 0.275 and 0.062 mM for G6PDH2, respectively. The pH optimum was 8.2 for G6PDH1 and 7.8 for G6PDH2. The enzyme is absolutely specific for NADP. NADPH is a competitive inhibitor of the G6PDH1 in respect to glucose-6-phosphate (G6P) and NADP (Ki = 0.050 and 0.025 mM, respectively). NADPH is a competitive inhibitor of the G6PDH2 in respect to NADP (Ki = 0.010 mM), but a non-competitive inhibitor in respect to the G6P. ADP, AMP, UTP, NAD, and NADH had no effect on the activity of G6PDH. ATP inhibited the G6PDH2 activity. and A. Semenihina ... [et al.].