Saturated amines and diamines as substrates which inhibit beef liver mitochondrial monoamine oxidase

Abstract

Monoamines and diamines of 8–12 carbon atoms initially serve as substrates for purified beef liver monoamine oxidase but then lead to inhibition. The inhibition is not solely the result of aldehyde formation as addition of decylaldehyde does not inhibit benzylamine oxidation. Furthermore, neither the addition of alcohol dehydrogenase and NADH nor of semicarbazide prevent the inhibition of diaminodecane oxidation. The formation of a Schiff base on the enzyme surface resulting in aggregation or occlusion of the enzyme may be a cause of the inhibition. When concentrated enzyme solutions (≥1 mg/ml) are reduced by long-chain amines, 100% O₂ causes only partial return of the flavin peak at 450 nm while enzyme activity continues to decrease. Substantial recovery of activity occurs (over a 3–4 week period) when inhibited enzyme is sedimented and resuspended in fresh buffer. These observations are discussed and compared with inhibition observed by other investigators with the substrate phenylethylamine.