Kinetic Characterization of Soybean Seedling Amine Oxidase

The kinetic characterization of soybean seedling amine oxidase (SSAO) and the effect of ionic strength and pH on the enzyme activity have been studied. A strong dependence of the activity on the carbon chain length of α–ω diamines, peaking at C8and at C5, forKmandkc, respectively, was found. The analysis of ionic strength effects on activity showed a high sensitivity ofKmand an insensitivity ofkcto this parameter. This behavior and the different dependence ofKmandkcon the carbon chain length suggest a two-stage equilibrium model for the oxidative deamination of polyamines by SSAO. The formation of the first intermediate (complex amine–enzyme) is controlled mainly by ionic interactions and by the structure of the polyamine, while the formation of the second intermediate depends only on the length of the carbon chain of the diamine. The molecular dissociation constants of the system soybean seedling amine oxidase–cadaverine were obtained from the dependence ofkc,Km, andkcKmon pH. A mechanism of the initial steps of reaction, involving a two-stage equilibrium model, is proposed.