Thyroid hormone binding by a component of mitochondrial membrane.

Area of Science:

• Molecular Biology
• Cellular Biology
• Endocrinology

Background:

• Thyroid hormone (triiodothyronine) is known to bind to intranuclear proteins, stimulating DNA transcription.
• Evidence suggests thyroid hormones also act directly on mitochondria, implying the existence of mitochondrial thyroid hormone-binding proteins.

Purpose of the Study:

• To investigate and demonstrate the presence of specific proteins that bind thyroid hormones within mitochondria.

Main Methods:

• Rat livers were homogenized, and mitochondria were isolated via sedimentation in 0.25 M sucrose.
• Mitochondria were washed multiple times to remove microsomes.
• Binding assays were performed using increasing concentrations of triiodothyronine and [125I]triiodothyronine.

Main Results:

• Strong binding of thyroid hormones was observed in both mitochondrial membranes and matrix fractions.
• The mitochondrial matrix infrequently displayed specific, saturable receptor sites for triiodothyronine.
• A strong 'nonspecific' interaction was typically observed in the mitochondrial matrix.

Conclusions:

• Mitochondria possess components, particularly in membranes and matrix, that bind thyroid hormones.
• While specific saturable receptors are not consistently found in the matrix, significant hormone binding occurs.