{'fraction_non_alphanumeric': 0.03412073490813648, 'fraction_numerical': 0.003937007874015748, 'mean_word_length': 5.407563025210084, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
The sialic acids. XV. Transfer of sialic acid to glycoproteins by a sialyltransferase from colostrum.

Abstract A soluble sialyltransferase was partially purified from colostrum (goat, bovine, and human). This enzyme catalyzed the transfer of sialic acid from cytidine monophospho-sialic acid to β-d-galactopyranosides. When N-acetyllactosamine was the acceptor, the products formed by the colostrum transferase contained sialic acid linked only to C-6 of the galactose moiety; with lactose as the acceptor, a small fraction of the sialic acid was linked to C-3 as well. These results distinguish the colostrum enzyme from the previously reported rat mammary gland sialyltransferase, which synthesized only the C-3 isomers of sialyllactose and sialyl-N-acetyllactosamine. In addition, the colostrum enzyme exhibited the following important specificity requirements towards the acceptor: (a) high, rather than low molecular weight substrates were much more effective; (b) the penultimate sugar to which galactose was linked in disaccharides markedly influenced the kinetic parameters (Vmax and Km); and (c) the position of linkage of galactose to the penultimate sugar resulted in 40-fold changes in the rate of the reaction. The most active disaccharide was N-acetyllactosamine (4-O-β-d-galactopyranosyl-N-acetylglucosamine). This disaccharide is a structural component of many glycoproteins, and it is suggested that the colostrum sialyltransferase catalyzes the final step in the synthesis of the serum-type glycoproteins.