Cytochrome P450 enzymes naming

The major mono oxygenases in the endoplasmic reticulum are cytochrome P450s—so named because the enzyme was discovered when it was noted that preparations of microsomes that had been chemically reduced and then exposed to carbon monoxide exhibited a distinct peak at 450 nm. Among reasons that this enzyme is important is the fact that approximately 50% of the drugs humans ingest are metabolized by isoforms of cytochrome P450 these enzymes also act on various carcinogens and pollutants. 

The cytochrome P450 enzyme family contains at least 100 to 150 different isozymes with at least 40% sequence homology. These isozymes have different but overlapping specificities. The human enzymes are generally divided into six major subfamilies, and each of these is further subdivided. For example, in the naming of the principal enzyme involved in the oxidation of ethanol to acetaldehyde, CYP2E1, the CYP denotes the cytochrome P450 family, the 2 denotes the subfamily, the E denotes ethanol, and the 1 denotes the specific isozyme. 

Pretreatment with rifampicin 600 mg once daily for 7 days reduced the AUC of erlotinib by about 66%. In another study, the AUC of a single 450-mg dose of erlotinib, taken after 11 days treatment with rifampicin was about 57% of that of erlotinib 150 mg taken without rifampicin. The manufacturers advise that alternative treatments with no cytochrome P450 enzyme-inducing activity should be considered. If this is not possible, the starting dose of erlotinib should be adjusted to 300 mg (UK) with close monitoring, and, if tolerated, further increased after 2 weeks, in 50 mg increments, to 450 mg. They also advise caution with other CYP3A4 inducers, and specifically name barbiturates, carbamazepine, phenobarbital, phenytoin, rifabutin, rifapentine, and St John s wort. 

Cytochrome P450 enzymes in the liver, particularly one called CYP2A6, metabolize it, mainly to cotinine (the name comes from an anagram of nicotine). 

An important enzyme in bio logical electron transport called cytochrome P450 gets Its name from its UV absorp tion The P stands for pig ment because it is colored and the 450 corresponds to the 450 nm absorption of one of Its derivatives... 

Cytochrome P450 monooxygenases are characterized through the presence of the heme (protoporphyrin IX) prosthetic group (Scheme 10.1) that is coordinated to the enzyme through a conserved cysteine ligand. They have obtained their name from the signature absorption band with a maximum near 450 nm in the difference spectrum when incubated with CO. The absorption arises from the Soret Jilt transition of the ferrous protoporphyrin IX-CO complex. 

Recall that one of the key drug-metabolizing enzymes is the cytochrome P450 (CYP450) enzyme called 1A2. Two atypical antipsychotic drugs are substrates of 1A2, namely olanzapine and clozapine. That means that when they are given con-... 

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