Bovine liver mitochondrial monoamine oxidase is not an iron-dependent enzyme.

Abstract

It has been reported that rat liver monoamine oxidase is an iron-dependent enzyme. Calculations from reported data suggest that rat liver monoamine oxidase contains 2 g atoms of iron/mol of enzyme. However, our data over a 16-year period show that our purified bovine liver monoamine oxidase does not contain sufficient iron to justify being considered an iron protein. In order to ensure the correctness of the iron content, two microchemical analyses and atomic absorption spectroscopy were used to determine the iron content of wet ashed samples. The iron content was also determined during successive steps of enzyme purification and was found to decrease rather than increase. Monoamine oxidase, being a hydrophobic outer membrane enzyme, is very difficult to purify and detailed tests for homogeneity are necessary. Our preparations show a single band when examined by sodium dodecyl sulfate-polyacrylamide disc electrophoresis and behave as a pure protein by end group analysis. Thus, bovine liver monoamine oxidase is not an iron-dependent enzyme.