Abstract
Chloroplast development in cotyledons differs in a number of ways from that in true leaves, but the cotyledon-specific program of chloroplast biogenesis has not been clarified. The cyo1 mutant in Arabidopsis thaliana has albino cotyledons but normal green true leaves. Chloroplasts develop abnormally in cyo1 mutant plants grown in the light, but etioplasts are normal in mutants grown in the dark. CYO1 has a C4-type zinc finger domain similar to that of Escherichia coli DnaJ. Recombinant CYO1 accelerates disulfide bond reduction in the model substrate insulin and renatures RNase A, indicating that CYO1 has protein disulfide isomerase activity. In this study, we analyzed the kinetics of CYO1 in detail. The optimum temperature and pH of CYO1 were 40˚C and pH 6.7, respectively. Since the [S]-[V] plot was sigmoid, CYO1 should be an allosteric enzyme. To determine the amino acids important for CYO1 activity, we generated a series of 7 point mutations of cysteine residues in CYO1, and report these results.
