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Phase 1 - Functionalization of compounds- Type : organism-specific biosystem
- 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.
- Organism: Homo sapiens
- Source : REACTOME [REACT_13705]
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