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Monoamine oxidase inhibitory modulators in rat heart cytosol: evidence for induction by thyroid hormone
Abstract:
Inhibitory modulators of monoamine oxidase (MAO) were found in rat heart 105,000 X g supernatant. The modulators inhibited MAO activity present in the outer mitochondrial membrane. The inhibition was noncompetitive when using membrane-associated MAO as enzyme source. The modulators did not, however, inhibit the enzyme activity in the soluble fraction prepared from outer mitochondrial membranes. MAO inhibitory modulator concentration in rat heart cytosol was increased by the administration of T4 to rats. Three different inhibitory molecules were identified by gel filtration studies. These results suggest that thyroid hormone regulates membrane-associated MAO activity via the production of MAO inhibitory modulators, that the modulators probably bind to specific sites on the outer mitochondrial membrane, and that this binding of modulators to the membranes may result in a structural change in the mitochondrial membrane and a decrease in MAO enzyme activity.
Insights
Thyroid hormone (T4) increases monoamine oxidase (MAO) inhibitory modulators in rat hearts. These modulators noncompetitively inhibit membrane-associated MAO, suggesting thyroid hormone regulates MAO activity through these specific mitochondrial membrane-binding molecules.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- Monoamine oxidase (MAO) is crucial for neurotransmitter metabolism.
- MAO activity is localized to the outer mitochondrial membrane.
- Regulation of MAO activity by thyroid hormones is not fully understood.
Purpose of the Study:
- To investigate the presence and function of MAO inhibitory modulators in rat heart cytosol.
- To determine the effect of thyroid hormone administration on these modulators.
- To elucidate the mechanism by which these modulators affect MAO activity.
Main Methods:
- Differential centrifugation to isolate mitochondrial fractions.
- Enzyme activity assays for MAO.
- Gel filtration chromatography for modulator identification.
- Administration of thyroxine (T4) to rats.
Main Results:
- MAO inhibitory modulators were identified in rat heart 105,000 x g supernatant.
- These modulators noncompetitively inhibited membrane-associated MAO but not soluble MAO.
- T4 administration increased the concentration of MAO inhibitory modulators in rat heart cytosol.
- Three distinct inhibitory molecules were characterized by gel filtration.
Conclusions:
- Thyroid hormone (T4) regulates membrane-associated MAO activity through the production of specific inhibitory modulators.
- These modulators likely bind to unique sites on the outer mitochondrial membrane.
- Modulator binding may induce conformational changes in the mitochondrial membrane, decreasing MAO enzyme activity.