Involved in the biosynthesis of benzylisoquinoline alkaloids (PubMed:16034588, PubMed:22725256, PubMed:23738019). Catalyzes the transfer of the methyl group to the 4'-hydroxyl group of 3'-hydroxy-N-methylcoclaurine to form reticuline (PubMed:16034588). Can also use laudanosoline and, with a lower activity, 6-O-methylnorlaudanosoline and norlaudanosoline as substrates (PubMed:16034588). Also involved in the papaverine biosynthesis (PubMed:22725256, PubMed:23738019). (S)-3'-hydroxy-N-methylcoclaurine + S-adenosyl-L-methionine = (S)-reticuline + H(+) + S-adenosyl-L-homocysteine Optimum pH is 7.0. Optimum temperature is 40 degrees Celsius. Alkaloid biosynthesis; (S)-reticuline biosynthesis; (S)-reticuline from (S)-norcoclaurine: step 4/4. Homodimer. Expressed in roots, stems, leaves and flowers (PubMed:12946416). Transiently induced from 4 to 7 days after seed imbibition. Up-regulated upon fungal elicitor treatment or wounding. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family. COMT subfamily.