an alpha-L-Fuc-(1->2)-beta-D-Gal-(1->4)-beta-D-GlcNAc derivative + GDP-beta-L-fucose <=> an alpha-L-Fuc-(1->2)-beta-D-Gal-(1->4)-[alpha-L-Fuc-(1->3)]-beta-D-GlcNAc derivative + GDP + H(+)
an alpha-l-fuc-(1->2)-beta-d-gal-(1->4)-beta-d-glcnac derivative + gdp-beta-l-fucose <=> an alpha-l-fuc-(1->2)-beta-d-gal-(1->4)-[alpha-l-fuc-(1->3)]-beta-d-glcnac derivative + gdp + h(+)