P450 enzymes cloned human

White JA, Beckett-Jones B, Guo YD, Dilworth FJ, Bonasoro J, et al. 1997. cDNA cloning of human retinoic acid-metabolizing enzyme (hP450RAI) identifies a novel family of cytochromes P450. J Biol Chem 272 18538-18541. 

The human hepatic cytochromes as expressed in this system demonstrate substrate specificities and enzymatic rates which are essentially comparable to the enzymes studied in human liver micro-somes and extracts. Membrane preparations derived from the Dundee P450 System retain cytochrome activity which is useful in simple biochemical assessments of substrate-enzyme interactions. Whole bacterial cells can be manipulated to explore the effects of substrate concentration and competition for co-factors and co-en-zymes through the appliance of molecular genetics. The same clones can be directed to the analytical scale production of meta-bohtes with benefits for the progression of dmg development programmes (see Tab. 

Direct information about the catalytic specificity of human P450 4B1 has been difficult to obtain because of problems in heterologous expression. Following the initial cDNA cloning, expression in a baculovirus system was unsuccessful and only yielded inactive cytochrome P420 (ref [971]). The substitution S427P allowed for expression, and lauric acid could be demonstrated. However, information about the native human enzyme has not been available (the S427P mutant does not occur naturally ). 

An expression-cloning approach was utilized to isolate a cDNA from Cyp7bl ) mice that could, when expressed, catalyze the 7a-hydroxyla-tion of 24-hydroxycholesterol . P450 39 has a microsomal location with a preference for the substrate 24-hydroxycholesterol and is expressed in liver. Presumably these characteristics of mouse P450 39 apply to the human ortholog but no further information is yet available. Potential relevance of this enzyme is in the inactivation of... 

An expression cloning approach was utilized to clone cDNAs encoding both murine and human cholesterol 24-hydroxylase, P450 46A1 (ref. [1475]). The mouse and human sequences are 95% identical. Expression is predominantly in brain (neurons in several regions). The enzyme is in the endoplasmic reticulum alternate substrates have not been explored but may be unlikely. 

---