Tetramethylammonium-corrinoid protein Co-methyltransferase (, mtqB (gene), tetramethylammonium methyltransferase) is an enzyme with systematic name tetramethylammonium:5-hydroxybenzimidazolylcobamide Co-methyltransferase. This enzyme catalyses the following chemical reaction
This enzyme is involved in methanogenesis from tetramethylammonium.