Monoamine Oxidase and Phenol

Monoamine oxidase catalyzes the conversion of dopamine to 3,4-dihydroxy-phenylacetic acid and tyramine to 4-hydroxyphenylacetic acid. Phenol sulfo- 

Radiolabeled products were separated from substrates by chromatography on a Merck Qg column (5 /an). The mobile phase contained 0.1 M sodium acetate, 0.1 M citric acid, 0.1 mAf sodium octylsulfate, 0.15 mAf EDTA, and 0.2 mAf dibutylamine in 10% methanol (v/v). The pH was 4 for the monoamine oxidase assay and 3.7 for phenol sulfotransferase. A flow-through radioisotope detector was used to quantitate the amount of radioactivity in the eluted peaks. 

The assay for monoamine oxidase contained in a final volume of 100 pL to 30 pL of homogenate and 50 pAf [7-14C] dopamine (0.93 mCi/mmol) or [7-,4C] tyramine (3.11 mCi/mmol) in 0.5 M phosphate buffer (pH 7.4). The assay for phenol sulfotransferase was also initiated by adding 30 pL of homogenate. The mixture contained 1.7 pAf [35S] 3 -phosphoadenosine-5 -phosphosulfate (1.51 Ci/mmol) and 50 pAf dopamine, 3,4-dihydroxyphenylacetic acid, or phenol in 10 mAf phosphate buffer (pH 6.4). After various incubation periods, the activity of either enzyme was stopped by addition of 30 pL of 2 N HC1. The resulting mixtures were centrifuged or filtered before analysis by HPLC. 

Half of a rat brain hypothalamus (8.5-10 mg), the anterior pituitary (5-7 mg), or minced liver (4 mg) was homogenized by sonicating in 100 pL of 0.5 Af phosphate buffer (pH 7.4) for the assay of monoamine oxidase, or in pH 6.4 buffer for assay of phenol sulfotransferase. 

N-Acetyltransferase uses acetyl-CoA to acetylate the amino moiety of arylal-kylamines. In mammalian pineal gland, this enzyme catalyzes the production of N-acetyl-5-hydroxytryptamine, which is the precursor of melatonin. It is also involved in the inactivation of monoaminergic neurotransmitters in insects. 

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