Further studies on a highly purified glycoprotein from the intimal region of procine aorta

Highly purified glycoprotein from the intimal region of porcine aorta was isolated with minor modifications of the procedure described previously. The molecular weight of the glycoprotein as determined by sedimentation equilibrium method either in presence of 0.1 M NaCl or 6 M guanidine-HCl containing beta-mercaptoethanol was 72 000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the native glycoprotein and its S-carboxyamidomethyl derivative at different acrylamide concentrations showed no difference in the molecular weight indicating the absence of subunits. Attempts to determine the identity of the amino-terminal acid by a dansylation technique indicated that the amino group is not free. The carboxy-terminal amino acid was found to be serine after treatment of the glycoprotein with carboxypeptidase A. The glycoprotein did not contain an alkali-labile (O-glycosidic) carbohydrate-protein linkage as tested by the beta-elimination reaction. The release of monosaccharides from the glycoprotein as a function of time was studied employing mild acid hydrolysis (0.5 M HCl, 80 degrees C) and also by the use of neuraminidase, alpha-D-and beta-D-glucosidases and beta-D-N-acetylglucosaminidase. From the observations of the release of monosaccharides and analogy with standard features determined by other investigators on soluble aortic glycoproteins, a prediction has been made as to the general features of the carbohydrate moiety of the glycoprotein.