Sequences are from: B. subtilis (Bs, P08064), W. succinogenes (Ws, P17413) N. pharaonis (Np, Y07709), T. acidophilum, (Ta, X70908), B. taurus (Bt, P35720, U50987), E. coli SQR (EcS, P10466, P10445), P. denitrificans (Pd, U31902), C. burnettii, (Cb, L33409), Rickettsia prowazekii (Rp, P41085), R. americana, (Ra, [36]), C. caldarium, (Cca, P48935, only SdhC), A. suum, (As, [164], only SdhD), P. purpurea, (Pp, [36]) C. crispus, (Ccr, P48934), M. polymorpha, (Mp, P35721, M68929) S. cerevisiae (Sc, P33421, P37298), E. coli QFR (EcQ, P03805, P03806), H. influenzae, (Hi, P44892, P44891) and M. tuberculosis (Mt, Q10762, Q10763).