ABSTRACT
The cytochromes P450 superfamily of heme-thiolate enzymes is known currently to comprise over 300 different proteins† which have been classified into 36 families and subfamilies based on their amino acid sequence homologies (Nebert et al., 1989, 1991a; Nelson et al., 1993). The most recently published update on nomenclature of P450 protein sequences, usually obtained from cDNA determinations, lists some 220 distinct P450 genes and their derived proteins (Nelson et al., 1993) of which 213 amino acid sequences have been aligned according to percentage similarity (Nelson, 1993). However, several groups have reported sequence alignments for smaller numbers of P450s which differ from each other to some degree depending on the methods used for aligning and the particular sequences involved (Kalb and Loper, 1988; Nelson and Strobel, 1988, 1989; Edwards et al., 1989; Gotoh and Fujii-Kuriyama, 1989; Tretiakov et al., 1989; Gotoh, 1992; Lewis and Moereels, 1992; Korzekwa and Jones, 1993; Haseman et al., 1995; Lewis, 1995a; Lewis and Lake, 1995).
