Catalyzes the conversion of tetrahydrocolumbamine to (S)-tetrahydropalmatine and of columbamine to palmatine, an isoquinoline alkaloid. columbamine + S-adenosyl-L-methionine = H(+) + palmatine + S-adenosyl-L-homocysteine (S)-tetrahydrocolumbamine + S-adenosyl-L-methionine = H(+) + S-adenosyl-L-homocysteine + tetrahydropalmatine Alkaloid biosynthesis; palmatine biosynthesis; palmatine from columbamine: step 1/1. Homodimer. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family. COMT subfamily.