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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.
Insights
Bovine liver monoamine oxidase is not iron-dependent, contrary to previous reports on rat liver enzymes. Rigorous purification and analysis confirmed low iron content, indicating it is not an iron protein.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Previous studies suggested rat liver monoamine oxidase (MAO) is an iron-dependent enzyme.
- Calculations indicated 2 g atoms of iron per mole of rat liver MAO.
Purpose of the Study:
- To investigate the iron content of purified bovine liver monoamine oxidase (MAO).
- To determine if bovine liver MAO is an iron-dependent enzyme.
Main Methods:
- Purification of bovine liver MAO over a 16-year period.
- Microchemical analyses and atomic absorption spectroscopy for iron content determination.
- Sodium dodecyl sulfate-polyacrylamide disc electrophoresis and end group analysis for homogeneity testing.
Main Results:
- Purified bovine liver MAO showed insufficient iron content to be classified as an iron protein.
- Iron content decreased during successive purification steps, not increased as expected for an iron-containing enzyme.
- Homogeneity tests confirmed the enzyme preparations were pure.
Conclusions:
- Bovine liver monoamine oxidase is not an iron-dependent enzyme.
- The enzyme's hydrophobic nature and outer membrane localization contribute to purification challenges.
- Previous assumptions about MAO iron dependency may be specific to certain species or require re-evaluation.