Amino-acid sequence of the cytochrome c3 (Mr 26 000) from Desulfovibrio desulfuricans Norway and a comparison with those of the other polyhemic cytochromes from Desulfovibrio

Abstract The amino-acid sequence of an octaheme cytochrome c 3 isolated from Desulfovibrio desulfuricans Norway is presented. The protein molecule ( M r 26 000) comprises two identical subunits of 111 amino acids with the characteristics typical of tetrahemic cytochrome c 3 class. Comparisons between the amino-acid sequences and physiological properties of cytochrome c 3 ( M r 26 000) and cytochromes c 3 ( M r 13 000) isolated from various species of Desulfovibrio showed the existence of considerable differences. In order to distinguish between the various subclasses in the cytochrome c 3 superfamily, the amino-acid sequence of cytochrome c 3 ( M r 26000 ) was compared with six known cytochrome c 3 ( M r 13000 ) sequences as well as with the sequence of the four c 3 -like domains of a high molecular weight cytochrome c (Hmc) containing 16 hemes per molecule of 65 500 Da, isolated from Desulfovibrio vulgaris Hildenborough. The evolution and phylogenetic relationships of these various polyhemic cytochromes are discussed.