Association of betaine-homocysteine S-methyltransferase with microtubules

In mammals, betaine of the mitochondrial matrix is used in the cytosol by b etaine-homocysteine S-methyltransferase for methionine synthesis. The resul ting dimethylglycine is shuttled back into the mitochondrial matrix for fur ther degradation. Nanospray tandem mass spectrometry and N-terminal amino a cid sequencing of microtubule-associated proteins from rat liver tubulin re vealed that betaine-homocysteine S-methyltransferase is microtubule associa ted. This was confirmed by confocal laser scanning microscopy of HepG2 cell s labeled with betaine-homocysteine S-methyltransferase- and alpha-tubulin- specific monoclonal antibodies. The association of betaine-homocysteine S-m ethyltransferase with the cytoskeleton may functionally integrate the mitoc hondrial and cytoplasmic compartments of choline degradation.