P450 cytochromes are the most important Phase 1 reactions. The reaction exposes a "handle" on an ingested drug. Phase 2 reactions involve the formation of a link between the "handle" of the drug and a conjugate via a transferring enzyme, a transferase. The most abundant conjugate is glucuronic acid and the "hooking" enzyme is uridine diphosphate glucuronyl transferase (UGT).
A classification system similar to the P450 CYPs has been developed to characterize the UGT superfamily of enzymes. There are 2 clinically significant UGT subfamilies UGT1A and UGT2B. In the liver, the most important UGTs found to date are UGTA1, 1A4,1A6, 1A9, 2B4, 2B7 2B11 and 2B15. In the same way that drugs can be substrates, inhibitors or inducers of CYPs, so too can they be substrates, inhibitors or inducers of UGTs and they may be handled by multiple UGT pathways.
The UGT table shows the current state of knowledge about UGT substrates, inducers and inhibitors. This data is in included in the P450+ Drug Interactions program.