Cytochrome endogenous

The numerous biotransformations catalyzed by cytochrome P450 enzymes include aromatic and aliphatic hydroxylations, epoxidations of olefinic and aromatic structures, oxidations and oxidative dealkylations of heteroatoms and as well as some reductive reactions. Cytochromes P450 of higher animals may be classified into two broad categories depending on whether their substrates are primarily endogenous or xenobiotic substances. Thus, CYP enzymes of families 1-3 catalyze... 

At least six isoforms of cytochrome P450 are present in the endoplasmic reticulum of human hver, each with wide and somewhat overlapping substrate specificities and acting on both xenobiotics and endogenous compounds. The genes for many isoforms of P450 (from both humans and animals such as the rat) have been isolated and smdied in detail in recent years. 

All cytochrome P450s are hemoproteins and generally have a wide substrate specificity, acting on many exogenous and endogenous substrates. They represent the most versatile biocatalyst known. 

Llerena A et al. Relationship between personality and debrisoquine hydroxyla-tion capacity. Suggestion of an endogenous neuroactive substrate or product of the cytochrome P4502D6. Acta Psych Scand 1993 87(l) 23-28. 

A further promising attempt to identify the bluelight-reducible cyt b is described by Britz et al.26) for a plasma-membrane-enriched fraction of com coleoptiles. They find that methylene blue (Scheme 2) is capable of reducing a particular cyt b which constitutes only 10—20% of the total dithionite-reducible cytochromes. Since this particular cyt b is very similar to that which is photo-reduced by endogeneous flavin in Neurospora 122,123) the two are proposed to be identical. 

All tissues except mature red blood cells are able to manufacture haem for use in the respiratory cytochrome proteins of the electron transport chain. However, the liver is an especially important site of haem synthesis because it (a) is a major organ of erythropoiesis in utero and (b) haem-containing cytochrome-P450 (CYP-450) enzymes play significant roles in hepatic detoxification of drugs, toxins and endogenous waste products (Section 6.4). 

Much work has demonstrated the presence of complex multienzyme monooxygenase systems within the endoplasmic reticulum of several mammalian species (for Reviews 1, 2, 3). These monooxygenase systems are responsible for the oxidative metabolism of many exogenous and endogenous substances, and the unusual non-specificity of these monooxygenase enzymes allows the metabolism of compounds with diverse chemical structures. Early work demonstrated that the terminal microsomal oxidase involved in xenobio-tic biotransformation was a hemoprotein, which has been subsequently named cytochrome P-450. 

Cytochromes P450 with primarily endogenous function in human brain (Amruthesh et al., 1992 Degtyarenko and Fabian, 1996 Nelson, 1998 Chang and Kam, 1999 Omiecinski etal., 1999 Nebertand Russell, 2002 Stoffel-Wagner, 2003)... 

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