label: 3-O-[N-acetyl-alpha-D-galactosaminyl]-L-threonyl-[protein] + UDP-N-acetyl-alpha-D-glucosamine => 3-O-[N-acetyl-beta-D-glucosaminyl-(1->3)-N-acetyl-alpha-D-galactosaminyl]-L-threonyl-[protein] + UDP + H(+)
label_lc: 3-o-[n-acetyl-alpha-d-galactosaminyl]-l-threonyl-[protein] + udp-n-acetyl-alpha-d-glucosamine => 3-o-[n-acetyl-beta-d-glucosaminyl-(1->3)-n-acetyl-alpha-d-galactosaminyl]-l-threonyl-[protein] + udp + h(+)