Involved in the biosynthesis of benzylisoquinoline alkaloids. Catalyzes the transfer of the methyl group to the 4'-hydroxyl group of 3'-hydroxy-N-methylcoclaurine to form reticuline. Also involved in the papaverine biosynthesis. (S)-3'-hydroxy-N-methylcoclaurine + S-adenosyl-L-methionine = (S)-reticuline + H(+) + S-adenosyl-L-homocysteine Alkaloid biosynthesis; (S)-reticuline biosynthesis; (S)-reticuline from (S)-norcoclaurine: step 4/4. Expressed in roots, stems, leaves and flowers (PubMed:12946416, PubMed:16813579). Restricted to sieve elements of the phloem adjacent or proximal to laticifers (PubMed:16813579). 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.