Glycosyltransferases of Canine Respiratory Tissue

Four monosaccharide glycosyltransferases have been found to be present in particles prepared from normal canine respiratory tissue, and this report describes some of their properties. One is a sialyltransferase which catalyzes the transfer of sialic acid from cytidine monophosphate N-acetyl-neuraminic acid to glycoproteins containing N-acetylgalactosamine as terminal residues. Another transferase found in these particles catalyzes the transfer of N-acetylglucosamine from its uridine diphosphate derivative to fetuin from which sialic acid, galactose, and N-acetylglucosamine had been removed. Several other glycoproteins were tested for acceptor activity and all were negative which shows the high specificity of this hexosaminyltransferase. This particulate preparation also catalyzed the transfer of fucosyl units from its sugar nucleotide to fetuin sequentially treated with sialidase and galactosidase. The fourth transferase, an N-acetylgalactosaminyltransferase, catalyzes the transfer of N-acetylgalactosamine from its uridine diphosphate derivative to a polypeptide prepared by treating ovine submaxillary mucin with sialidase and N-acetylgalactosaminidase. Porcine submaxillary mucin, free of the terminal N-acetyl-galactosamine residues, was also an acceptor for the latter sugar nucleotide which suggests the presence of a second N-acetylgalactosaminyltransferase in the particles. The presence of the latter enzyme infers that respiratory mucins contain the blood type A structural determinant. Enzymatic activities were stimulated by Triton X-100 and, except for the sialyltransferase by Mn2+. Maximum incorporation occurred at near neutral or slightly acidic pH, and the Km values for the substrates were found to be approximately 10-3 m. The activities of the transferases were inhibited by nucleotides and at moderate or high ionic strengths.