A method for stabilization of monoamine oxidases in homogenates of rat intestine epithelium

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Abstract
In a homogenate of epithelium isolated from the small intestine of male Wistar rats, the amine oxidase activity with 10−3M tyramine was 9200 ± 200 nmol (g tissue)−1 h−1 of which 91% was due to the A form of monoamine oxidase (MAO) and 9% to the B form. Semicarbazide-sensitive amine oxidase activity was not detected with either 10−3M tyramine or 10−4M benzylamine as substrate. However, it was detectable in the homogenate of the gut residue where the activity with 10−4M benzylamine was 3600±200 nmol (g tissue)−1 h−1. The MAO activity, in homogenates of epithelium prepared with 0.1 M sodium phosphate pH 7.4, was stable at 4°C for at least 6 h whilst at minus 20°C it decreased by 70% within 24 h. Incorporation of 10% (v/v) glycerol into the homogenization medium stabilized the enzymes. The total activity and proportions due to MAO-A and MAO-B and kinetic constants for tyramine and 5-hydroxytryptamine, did not alter during 5 weeks storage at −20°C. The ability to store tissue homogenates should facilitate studies of intestinal amine oxidases.