– Isoform 1 catalyzes the transfer of a methyl group onto N-acetylserotonin, producing melatonin (N-acetyl-5-methoxytryptamine). Isoform 2 and isoform 3 lack enzyme activity. ASMT Protein, Human, Recombinant (His & Myc) is expressed in E. coli expression system with N-10xHis and C-Myc tag. The predicted molecular weight is 45.9 kDa and the accession number is P46597.