AMINO-ACID-SEQUENCE OF THE CYTOCHROME-C(3) (M(R)26000) FROM DESULFOVIBRIO-DESULFURICANS NORWAY AND A COMPARISON WITH THOSE OF THE OTHER POLYHEMIC CYTOCHROMES FROM DESULFOVIBRIO

The amino-acid sequence of an octaheme cytochrome c3 isolated from Desulfovibrio desulfuricans Norway is presented. The protein molecule (M(r) 26000) comprises two identical subunits of 111 amino acids with the characteristics typical of tetrahemic cytochrome c3 class. Comparisons between the amino-acid sequences and physiological properties of cytochrome c3 (M(r) 26000) and cytochromes c3 (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 C3 superfamily, the amino-acid sequence of cytochrome c3 (M(r) 26 000) was compared with six known cytochrome c3 (M(r) 13 000) sequences as well as with the sequence of the four c3-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.