Colostrum, sialyltransferase activity

The basis for the multiplicity of the sialyltransferase activities remains to be elucidated. We plan to purify these enzyme species to homogeneity, using isoelectric focusing columns of smaller pH ranges in conjunction with affinity chromatography which has been successfully used to purify the soluble sialyl-transferases from bovine colostrum (57). Possibility exists that the heterogeneity of sialyltransferase activities as observed is due to differences in polypeptide sequences, carbohydrate content, or non-covalent interactions with other membrane components, and these possibilities can be clarified only with highly purified enzyme preparations. 

The two sialyltransferase activities have identical pH optima and Grimes (1970) suggests that a single enzyme may be involved. However, the colostrum glycoprotein sialyltransferase and the salivary gland mucin sialyltransferase are believed to be separate enzymes (Roseman et al, 1966), the former attaching sialic acid to terminal galactose resi-... 

The SAT that catalyzes the synthesis of sialyllactose was first detected in rat mammary tissue by Roseman and his co-workers (Jourdian et al., 1963 Carlson et al., 1973a). In fact, this was the first SAT to be characterized in an animal system, being detected later in embryonic chicken brain (Kaufman and Basu, 1966). However, the SAT activities that catalyze the transfer of sialic acid to lactose and to lactosylceramide appear to be different from the latter by all kinetic parameters (S. Basu, 1966 Kaufman and Basu, 1966 M. Basu et al., 1987 S. C. Basu, 1991). In addition to CMP-NeuAc lactose a2-3 sialyltransferase, CMP-NeuAc lactosamine a2-6 sialyltransferase (ST6N) was first characterized by Roseman and his co-workers (Bartholomew et al., 1973) from colostrum. The ST6N enzyme activity is ubiquitous and was purified by Hill and his associates... 

---