Distinction and Partial Characterization of Two Galactosyl-transferase Activities in Normal Human Serum

Abstract

Publisher Summary This chapter outlines the distinction and partial characterization of the two galactosyl transferase activities in normal human serum. Galactosyltransferase (GT) activity in human and animal sera has been extensively studied in relation to various pathophysiological conditions. Among the various correlations, serum GT activity has been found increased or qualitatively changed in cancer. Most work has been carried out with asialo-agalacto-fetuin (SGf-fetuin) as acceptor for Gal, under the assumption that this acceptor possesses only GlcNAc acceptor residues Spiro and Bhoyroo. The use of two different acceptors for Gal, namely ovalbumin and asialo-ovine submaxillary mucin (Sf-OSM), permits the distinction of two different GT activities in normal human serum. The result shows that the two GT activities in human serum could be distinguished by heat inactivation: GT-A assayed with Sf-OSM was reduced by 50% within 6 h at 37°C, whereas 48 h at 37°C was required to obtain a 50% loss of GT-B (assayed with ovalbumin). Striking differences between GT-A and GT-B in their acceptor specificities were found with small molecular weight acceptors and interacted with α-lactalbumin to form lactose with glucose as acceptor. In contrast, GT-A had similarly low affinities for both GalNAc and GlcNAc and did not interact with α-lactalbumin. The incorporation of Gal into Sf-OSM by GT-B could be inhibited completely.