Some current matters of monoamine oxidase biochemistry

Some problems in the basic biochemistry of monoamine oxidase (MAO) and the regulation of its concentration in tissues are considered. The substrate preferences of muscle MAO do not conform to the current distinction between A and B forms of the enzyme. Examples of this are given for skeletal and cardiac muscle. Although the enzyme concentration is low in this tissue, its relatively great mass suggests that it has a role to play in monoamine metabolism. The significance of riboflavin and iron for MAO activity is discussed.