J. Biochem, 1988, Vol. 104, No. 4 648-657
© 1988 Japanese Biochemical Society
research-article |
Sulfated Glycoproteins Synthesized by the Corneal Epithelium of Chick Embryo Having the Same Molecular Weights as Cytokeratin Polypeptides1
*Clinical Research Institute, National Nagoya Hospital Naka-ku, Nagoya, Aichi 460
**Department of Chemistry, Faculty of Science, Nagoya University Chikusa-ku, Nagoya, Aichi 464
***Aichi Cancer Research Institute Chikusa-ku, Nagoya, Aichi 464
****School of Medicine, Nagoya City University Mizuho-hu, Nagoya, Aichi 467
3To whom correspondence should be addressed
The previous study from this laboratory demonstrated that the corneal epithelium of 19-d-old chick embryo synthesizes two classes of sulfated glycoconjugates consisting of sulfated glycoproteins and proteoglycans (Yonekura, H., Oguri, K., Nakazawa, K., Shimizu, S., Nakanishi, Y., & Okayama, M. (1982) J. Biol. Chem. 257, 11166–11175). The present study demonstrated that when the sulfated glycoproteins labeled metabolically with [38S] sulfate and [3H] glucosamine were analyzed by SDS-PAGE, the 70,000 component (accounting for approximately 30% of the 355 and 35% of the 3H of the total sulfated glycoprotein) co-migrated with five major proteins with apparent molecular weights (MrS) of 70,000, 66,000, 58,000, 51,000, and 48,000, which together accounted for about 57% of the total tissue protein. All five proteins cross-reacted with an antibody against human sole keratin, indicating that they are cytokeratin polypeptides of the cornea! epithelium. Amino acid analysis demonstrated that they had high contents of glycine, serine, glutamic acid, leucine, and aspartic acid. Two-dimensional tryptic peptide maps indicated that they were all different. Analysis of radiolabeled materials released by alkaline borohydride treat ment of the sulfated glycoproteins which were synthesized in the presence and absence of tunicamycin and co-purified with the five cytokeratin polypeptides, revealed that they contained both N- and O-glycosidically linked sulfated oligosaccharides. All the results obtained in the present study indicate that the five sulfated glycoproteins are similar, if not identical, to the cytokeratin polypeptides. This is consistent with the result in the accompanying paper that these sulfated glycoproteins are localized intracellularly.
1This study was supported in part by a Grant-in-Aid for Cancer Research (60-4) from the Ministry of Health and Welfare of Japan, and by grants from the Foundation for Promotion of Cancer Research and The Fujisawa Foundation.
2Present address: Cell Engineering Creative Products Research Laboratories Research Institute, Kissei Pharmaceutical Co., Ltd, Matsumoto, Nagano 399.