Xenobiotic metabolism monoamine oxidase

A number of other enzymes, such as monoamine oxidase, alcohol dehydrogenase and xanthine oxidase, are also involved in drug metabolism. These enzymes tend to be more specific, oxidizing xenobiotics related to the normal substrate for the enzyme. 

Piperonyl butoxide, isoniazid, and SKF 525A and related chemicals are inhibitors of various xenobiot-ic-metabolizing enzymes. For instance, piperonyl butoxide increases the toxicity of pyrethrum (an insecticide) by inhibiting MFO activity in insects that detoxifies this agent. Isoniazid, when taken along with phenytoin, lengthens the plasma half-life of the antiepileptic drug and increases its toxicity. Iproniazid inhibits monoamine oxidase and increases the cardiovascular effects of tyramine, which is found in cheese and which is normally readily metabolized by the oxidase. 

This flavoprotein, which catalyzes the oxidative deamination of amines, functions in the breakdown of endogenously produced neurotransmitter amines. Vertebrate monoamine oxidase also catalyzes the oxidation of xenobiotic amines, particularly in tissues such as the intestine (4). Whether the schistosome enzyme is also capable of metabolizing xenobiotics has not been investigated. 

Other types of biological oxidation are catalyzed by more specific enzymes, which play an individual role in the metabolism (various specific dehydrogenases and oxidases) or in regulatory processes (e.g. monoamine oxidase inactivating some neurotransmitters) rather than coping with xenobiotics. However, many of these enzymes are soluble and may be present in the body fluids and come into contact with components even in the extracellular compartment. 

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