Rabbit Serum Monoamine Oxidase
PURIFICATION AND CHARACTERIZATION
Charles M. McEwen Jr. 1, Kenneth T. Cullen 1, and Arthur J. Sober 1
From the
1 From the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, United States Public Health Service, Bethesda, Maryland 20014
A monoamine oxidase has been identified in rabbit serum and purified approximately 450-fold by a procedure involving fractionation with ammonium sulfate and adsorption on calcium phosphate. The purified enzyme has an absorption maximum at 470 mµ, which is decreased in the presence of substrate. It oxidizes primary amines with the stoichiometric formation of the corresponding aldehydes, hydrogen peroxide, and ammonia. Substrates most actively oxidized by the enzyme are substituted phenylethylamines (e.g. dopamine, tyramine, mescaline) and C-arylmethylamines. Less actively oxidized substrates include tryptamine, serotonin, histamine, and simple aliphatic amines.
The effect of pH upon apparent Michaelis constants and maximal velocities of benzylamine oxidation has been studied. The results indicate that the protonated species of the amine interacts with the free enzyme and that this interaction is affected by an ionization (pKa 6.2) of the enzyme. An ionization (pKa 6.4 to 6.5) of the enzyme-substrate complex is a determinant of maximal velocities.
Submitted on April 4, 1966
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