Association of betaine-homocysteine S-methyltransferase with microtubules.

In mammals, betaine of the mitochondrial matrix is used in the cytosol by betaine-homocysteine S-methyltransferase for methionine synthesis. The resulting dimethylglycine is shuttled back into the mitochondrial matrix for further degradation. Nanospray tandem mass spectrometry and N-terminal amino acid sequencing of microtubule-associated proteins from rat liver tubulin revealed that betaine-homocysteine S-methyltransferase is microtubule associated. This was confirmed by confocal laser scanning microscopy of HepG2 cells labeled with betaine-homocysteine S-methyltransferase- and alpha-tubulin-specific monoclonal antibodies. The association of betaine-homocysteine S-methyltransferase with the cytoskeleton may functionally integrate the mitochondrial and cytoplasmic compartments of choline degradation.