Purification and characterization of a Neu5Ac.alpha.2 .fwdarw. 6Gal.beta.1 .fwdarw. 4GlcNAc and HSO3- .fwdarw. 6Gal.beta.1 .fwdarw. 4GlcNAc specific lectin in tuberous roots of Trichosanthes japonica