Catalyzes the O-methylation, and thereby the inactivation, of catecholamine neurotransmitters and catechol hormones (By similarity). Required for auditory function. Component of the 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:28534737). a catechol + S-adenosyl-L-methionine = a guaiacol + H(+) + S-adenosyl-L-homocysteine Enriched in an apical membrane compartment above the nucleus in the hair cells. Not detectable in the hair bundle. May be present at lower levels in the endoplasmic reticulum and the basolateral membrane. At 28 hr post-fertilization (hpf), expressed exclusively in the hair cells of the anterior and posterior maculae in the developing ear. At 4 days post-fertilization (dpf), expressed specifically in hair cells of the inner ear and lateral line organ. Originally identified in a genetic screen for genes required for hearing and balance. The mercury circler mutant phenotype is characterized by balance defects, an absence of the acoustic startle reflex, failure to inflate the swim bladder, lack of hair cell-dependent calcium responses in the hindbrain, and undetectable microphonic currents. No morphological defects in the sensory hair cell bundles nor epithelium. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-dependent O-methyltransferase family. Despite its name, the zebrafish TOMT protein is not predicted to contain a transmembrane region in contrast to primate orthologs.