Approximately a quarter of the 57 human CYPs still remain "orphans" in the sense that their function, expression sites, and regulation are largely not elucidated. While there is enough experimental evidence to know that all these proteins get made and can catalyze CYP-like reactions in vitro, evidence of in vivo function and substrate specificity is insufficient to allow them to be placed in any of the classes in the functional scheme.
|16126164||Function of human cytochrome P450s: characterization of the orphans||Biochem Biophys Res Commun||2005|
|15102545||57 varieties: the human cytochromes P450||Pharmacogenomics||2004|
|17786643||Characterization of orphan human cytochromes P450||Drug Metab Rev||2007|