a 3-O-[N-acetyl-alpha-neuraminyl-(2->3)-beta-D-galactosyl-(1->3)-N-acetyl-alpha-D-galactosaminyl]-L-threonyl-[protein] + CMP-N-acetyl-beta-neuraminate => a 3-O-{alpha-Neu5Ac-(2->3)-beta-D-Gal-(1->3)-[alpha-Neu5Ac-(2->6)]-alpha-D-GalNAc}-L-threonyl-[protein] + CMP + H(+)
a 3-o-[n-acetyl-alpha-neuraminyl-(2->3)-beta-d-galactosyl-(1->3)-n-acetyl-alpha-d-galactosaminyl]-l-threonyl-[protein] + cmp-n-acetyl-beta-neuraminate => a 3-o-{alpha-neu5ac-(2->3)-beta-d-gal-(1->3)-[alpha-neu5ac-(2->6)]-alpha-d-galnac}-l-threonyl-[protein] + cmp + h(+)