Site-directed Mutagenesis of epsilon Subunit of ATP Synthase of Maize Chloroplast.

The effects of some residues in maize chloroplast epsilon subunit on its activity have been studied by site-directed mutagenesis. After replacing Thr-42 of epsilon subunit with Cys, Arg, Ile or Pro, and forming the mutant epsilonT42C, mutant epsilonT42R, mutant epsilonT42I and mutant epsilonT42P respectively, it was found that the mutant epsilonT42P protein could no longer be expressed, but expression of other epsilon subunit mutants was similar to that of wild type. Comparing the inhibitory potency of different mutants of epsilon subunit with that of the wild type, it was found that the inhibitory effects of epsilon subunit mutants epsilonT42C and epsilonT42R on ATPase activity were slightly higher than that of wild type, but the epsilonT42I protein strongly inhibited the Ca(2+)-ATPase activity.