The specificity of sialyltransferase activity in smooth membrane fractions of embryonic chicken liver.
Smooth membrane preparations of 13-day embryonic chicken livers, characterized by electron microscopy and marker enzyme analyses, have been found to contain sialyltransferase activity which displayed precise acceptor specificity. One sialyltransferase transferred N-acetyl-neuraminic acid (NANA) and gal beta 1 leads to 4glycNAc beta 1 leads R structures. Evidence based on competition studies suggests that a second enzyme is present transferring this sugar to a gal beta 1 leads to 3gal-NAc alpha 1 leads to R structure. The enzyme capable of adding NANA to gal beta 1 leads to 4glcNAc beta 1 leads to R structures has a pH optimum of 5.5, a temperature optimum of 30 degrees C, and half-saturating values of 17 muM for CMP-NANA and 180 muM for galactoside termini on desialyzed alpha 1-acid glycoprotein. It is activated about 10-fold by Triton X-100, has no exogenous divalent cation requirement, and is inhibited by CTP, CDP, and CMP. The enzyme requires carbohydrate structures underlying the gal beta 1 leads to 4glcNAc terminus for maximal catalytic activity; the necessity of such precise specificities of sialyltransferases is discussed in the light of recent structural evidence for the carbohydrate moieties of several glycoproteins.
D000818:Animals; D002236:Carbohydrate Conformation; D002462:Cell Membrane / Q000201:enzymology; D002642:Chick Embryo; D004187:Disaccharides; D006023:Glycoproteins; D008099:Liver / Q000201:enzymology*; D012794:Sialic Acids; D012799:Sialyltransferases / Q000378:metabolism*; D013379:Substrate Specificity; D014166:Transferases / Q000378:metabolism*
D004187:Disaccharides; D006023:Glycoproteins; D012794:Sialic Acids; D014166:Transferases; D012799:Sialyltransferases