Multiglycosyltransferase System of Canine Respiratory Tissue

A galactosyltransferase has been found in a particulate preparation prepared from normal canine respiratory tissue which catalyzes the transfer of galactose from its uridine diphosphate derivative to N-acetylgalactosamine residues. The transfer to sialidase-treated ovine submaxillary mucin was dependent upon Mn*+ and was stimulated several-fold by Triton X-100. The optimal pH was between 6 and 7. The Km was 7 X lo-* M for UT@-galactose and 1 X lOma M for sialidase-treated ovine submaxillary mucin. Removal of the N-acetylgalactosamine residues on this acceptor reduced the incorporation of galactose. The enzyme was present throughout the airway passage with some evidence of higher activity in the lower portion of the trachea and the extrapulmonary primary bronchi. Fetuin from which sialic acid and galactose were removed was also an acceptor (K,,, = 0.9 X 10ea M). When the terminal N-acetylglucosamine residues were removed from this acceptor, the incorporation of galactose was reduced. No competition was demonstrated when this acceptor was mixed with sialidase-treated ovine submaxillary mu&; this suggests that there are at least two separate galactosyltransferases present in canine respiratory tissue or two catalytic sites on the same molecule.