MW: 37 kDa (328 aa), confirmed by MALDI-TOF. Purity >95% by SDS-PAGE. Histamine N-methyltransferase (HNMT) is found in the cytosol and uses S-adenosyl-L-methionine as the methyl donor. HNMT inactivates histamine by N-methylation. Histamine is involved in regulation and modulation of immune response through the stimulation of four distinct subtypes of receptors, H1, H2, H3, and H4, present on the target cells. Histamine is inactivated by the histamine-metabolizing enzyme histamine N-methyltransfe