Catalyzes the O-methylation, and thereby the inactivation, of catecholamine neurotransmitters and catechol hormones (PubMed:18794526). Required for auditory function (PubMed:18794526, PubMed:28504928). Component of the cochlear hair cell's mechanotransduction (MET) machinery. Involved in the assembly of the asymmetric tip-link MET complex. Required for transportation of TMC1 and TMC2 proteins into the mechanically sensitive stereocilia of the hair cells. The function in MET is independent of the enzymatic activity (PubMed:28504928). a catechol + S-adenosyl-L-methionine = a guaiacol + H(+) + S-adenosyl-L-homocysteine Interacts with LHFPL5, PCDH15, TMC1, TMC2 and TMIE (PubMed:28504928). The interaction of TOMT with TMC1 and TMC2 is required for the transportation of TMC1/2 into the stereocilia of hair cells (PubMed:28504928, PubMed:28534737). Interacts directly with TMC1 (PubMed:28534737). Localized to the cell body of the cochlear hair cells, but is not present in the stereocilia. Present but not restricted to the apical cistern, Hensen's body and the subsurface cistern. Widely expressed with high levels in outer and inner hair cells of the cochlea and vestibule. Not detected in the embryo at 12.5 dpc. At 14.5 dpc, expressed in the developing inner ear. At 16.5 dpc, expressed in the utricle and saccule. At 18.5 dpc, expressed specifically in the region of the sensory cells of the cochlea, utricle, saccule and crista ampullaris. Absence of auditory brain stem response (ABR) to click stimuli demonstrates that the mice are profoundly deaf. Normal hair bundle morphology as at postnatal day (P) 5 the sensory epithelia are patterned into three rows of outer hair cells (OHCs) and one row of inner hair cells (IHCs). The bundles of OHCs appear similar in size to those of wild-type mice and form a normal staircase pattern. Hair cells are maintained in the presence of gentamicin, an aminoglycoside antibiotic that enters hair cells through their transduction channels and normally causes hair cell death. No difference in the expression or localization of tip link proteins CDH23 and PCDH15 or ATP2B2, MYO7A, ESPN and WHRN proteins at P5-P8 in hair bundles of hair cells. Normal localization of LHFPL5 and TMIE in OHCs, but TMC1 and TMC2 are absent from the hair bundles of OHCs. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-dependent O-methyltransferase family. Despite its name, the murine TOMT protein does not contain a transmembrane region in contrast to primate orthologs.