Characterization and amino acid sequences of cytochromes c(6) from two strains of the green alga Chlorella vulgaris

Cytochromes c(6) from the green algae Chlorella vulgaris CK-5 (CK5cyc6) and C. vulgaris CR-22 (CK22cyc6) were characterized and their amino acid seque nces were analyzed. CK5cyc6 had a molecular mass of 9.3 kDa, isoelectric po ints of 3.0 (reduced) and 3.6 (oxidized), and a redox potential of +362 mV at pH 7.0. CK22cyc6 had a molecular mass of 9.5 kDa, isoelectric points of 2.9 (reduced) and 3.5 (oxidized), and a redox potential of +355 mV at pH 7. 0. The absorption spectra of both cytochromes c(6) showed 4 maxima in reduc ed form, and 2 maxima and a weak peak at 695 nm in oxidized form. The pyrid ine ferrohemochrome spectra indicated that their prosthetic group was heme c, These physicochemical properties were similar to those of other algal cy tochromes cs. The amino acids (88 residues) of CK5cyc6 and CK22cyc6 were se quenced and the sequence motif -CXXCH-, which is typical of the heme-bindin g site of c-type cytochrome, was clearly confirmed in both cytochromes. Twe nty-six amino acid residues were substituted, and the similarity score of e ach of them was 70.45%.