We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1-11, 1987; Nebert et al., DNA 8, 1-13, 1989; Nebert et al., DNA Cell Biol. 10, 1-14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. "P" ("p" in mouse) after the gene number denotes a pseudogene. If a gene is the sole member of a family, the subfamily letter and gene number need not be included. We suggest that the human nomenclature system be used for all species other than mouse. The mRNA and enzyme in all species (including mouse) should include all capital letters, without italics or hyphens. This nomenclature system is identical to that proposed in our 1991 update. Also included in this update is a listing of available data base accession numbers for P450 DNA and protein sequences. We also discuss the likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear. Finally, we describe P450 genes that have been detected by expressed sequence tags (ESTs), as well as the relationship between the P450 and the nitric oxide synthase gene superfamilies, as a likely example of convergent evolution.

The developmentally regulated expression of forms of cytochrome P-450, namely, those encoded by lambda HFL33 and NF25 or HLp cDNAs, which were isolated from respective fetal and adult human liver cDNA libraries, was investigated. When EcoRI fragments of cDNA clones of lambda HFL33 and NF25 were used as probes, these probes hybridized with RNA from both fetal and adult human livers. However, when oligonucleotides specific to the coding and 3'-noncoding region of lambda HFL33 (oli-HFL and oli-HFL3', respectively) were used as probes, these probes gave hybridizable bands with RNA from fetal but not adult livers. On the other hand, an oligonucleotide probe specific to the coding region of NF25 and HLp (oli-NF) gave positive bands with RNA only from adult livers. These results indicate that P-450(HFL33) is expressed specifically in fetal livers and that neither P-450NF nor HLp is expressed in fetal livers, but one or both are expressed in adult livers.

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Introduction Unlike experimental animals except monkeys, human fetal livers possess forms of cytochrome P-450. Since most of chemicals including drugs have been shown to penetrate placentas to reach fetuses at efficient rates, the pharmacological and toxicological significance of cytochrome P-450 may be regarded as one of most important research projects to be focused. If certain chemicals undergo metabolic activation by the fetal cytochrome P-450 and the metabolites are genotoxic in nature, then the use of rats and mice for the examination of genotoxicity of them may give no informations because of the lack of the activation enzymes. Therefore, in vitro cell systems as well as in vivo whole bodies such as transgenic animals which express human fetal enzymes will become powerful tools to predict possible embryo toxicity of chemicals. In the present communication, we would like to show our data on the expression of human fetal cytochrome P-450 for application to further characterization studies.Properties of cytochrome P-450 purified from human fetal livers We have purified four forms of cytochrome P-450, namely P-450HFLa, P-450HFLb, P-450HFLc and P-450HFLd, from human fetal livers. P-450HFLa and P-450HFLc possessed very high homology in their N-terminal amino acid sequences. The sequences suggested that these forms were classified into a family of P-450IIIA. P-450HFLa and P-450HFLc cross-reacted with polyclonal antibodies with each other.The immunochemical quantitation of P-450HFLa together with P-450HFLc indicated that these forms of cytochrome P-450 were major ones present in human fetal livers. P-450HFLd did not show any significant catalytic activities, while the remainders showed mutagen-producing activities from promutagens. The purified preparation of P-450HFLa catalyzed the 16a-hydroxylation of dehydroepiandrosterone 3-sulfate and the mutagenic activation of aflatoxin Bi. Using antibodies to P-450HFLa as a probe, we could isolate a cDNA clone coding for P-450HFLa. This was later termed as P-450IIIA7. The sequence of P-450IIIA7 cDNA was highly homologous to Ρ-450ΙΠΑ4 cDNA, which encoded P-450NF and was isolated from the cDNA library of human adult livers.Expression of P-450IIIA7 (P-450HFLa) in insect cells and examination for toxicological significance As mentioned above, we found that P-450HFLa is a major P-450IIIA form in human fetal livers. Thus, to examine the exact properties of P-450HFLa in the metabolic activation of 20 Brought to you by | University of Arizona Authenticated Download Date | 5/29/15 7:16 AM promutagens, we expressed this form of cytochrome P-450 in insect (Spodoptera frugiperda, Sf9) cells. P-450IIIA7 cDNA was first inserted to a BamH I site of a plasmid pAcYMl to obtain a recombinant plasmid pAcHFl. P-450IILA7 cDNA was further transferred to a AcNPV viral DNA by a homologous recombination to obtain recombinant virus NPVHF1. The Sf9 cells infected with NPVHF1 virus expressed P-450IIIA7 protein (P-450HFLa) to a specific content of approx. 1.1 nmole per mg of total lysate protein when ...