description
Phase 1 of metabolism is concerned with functionalization, that is the introduction or exposure of functional groups on the chemical structure of a compound. This provides a 'handle' for phase 2 conjugating species with which to react with. Many xenobiotics are lipophilic and almost chemically inert (e.g. PAHs) so would not necessarily undergo a phase 2 reaction. Making them more chemically reactive would facilitate their excretion but also increases their chance of reacting with cellular macromolecules (e.g. proteins, DNA). There is a fine balance between producing a more reactive metabolite and conjugation reactions.There are two groups of enzymes in phase 1 - oxidoreductases and hydrolases. Oxidoreductases introduce an oxygen atom into or remove electrons from their substrates. The major oxidoreductase enzyme system is called the P450 monooxygenases. Other systems include flavin-containing monooxygenases (FMO), cyclooxygenases (COX) and monoamine oxidases (MAO). Hydrolases hydrolyse esters, amides, epoxides and glucuronides

external resources
NCBI:1270190
REACTOME:R-HSA-211945
PUBMED:12369887
PUBMED:17125408
PUBMED:16584116

genes
AADAC , AOC1 , ADH1A , ADH1B , ADH1C , ADH4 , ADH5 , ADH6 , ADH7 , AHR , ALDH1A1 , ALDH2 , ALDH3A1 , ALDH1B1 , AOC2 , ARNT , BPHL , CBR3 , CES1 , CYP1A1 , CYP1A2 , CYP1B1 , CYP2A6 , CYP2A7 , CYP3A7 , CYP2A13 , CYP2B6 , CYP2C19 , CYP2C8 , CYP2C9 , CYP2C18 , CYP2D6 , CYP2E1 , CYP2F1 , CYP2J2 , CYP3A4 , CYP3A5 , CYP4A11 , CYP4B1 , CYP7A1 , CYP8B1 , CYP11A1 , CYP11B1 , CYP11B2 , CYP17A1 , CYP19A1 , CYP21A2 , CYP24A1 , CYP26A1 , CYP27A1 , CYP27B1 , CYP51A1 , CYB5R3 , EPHX1 , FDX1 , FDXR , FMO1 , FMO2 , FMO3 , HSP90AB1 , CYP4F3 , MAOA , MAOB , NQO2 , POMC , POR , PTGIS , PTGS1 , RXRA , TBXAS1 , CYP4F2 , AOC3 , NCOA1 , CES2 , AIP , CYP7B1 , ARNT2 , NR1H4 , NCOA2 , PTGES3 , CYP46A1 , CYP4F8 , CES3 , CYP2S1 , CYP39A1 , SMOX , CYP2W1 , MARC2 , ACSS2 , CYP26B1 , AHRR , CYP4F11 , MARC1 , CYP3A43 , CYP4F12 , CYB5B , ACSS1 , FDX2 , CYP2U1 , CYP2R1 , CYP4F22 , CMBL , PAOX , CYP4A22 , CYP4V2 , CYP26C1 , MIR4651 , CYP3A7-CYP3A51P ,