Involved in the regulation of homocysteine metabolism. Converts betaine and homocysteine to dimethylglycine and methionine, respectively. This reaction is also required for the irreversible oxidation of choline. glycine betaine + L-homocysteine = L-methionine + N,N-dimethylglycine Binds 1 zinc ion per subunit. Amine and polyamine degradation; betaine degradation; sarcosine from betaine: step 1/2. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-methionine from L-homocysteine (BhmT route): step 1/1. Homotetramer. Predominantly localized in the cytoplasm with a small fraction detected in the nucleus. Translocates into the nucleus upon oxidative stress. Found exclusively in liver and kidney.