Transient expression of sialylated glycans during glycoprotein processing by embryonal carcinomas.

Embryonal carcinoma and early embryonic cells express unusually large and complex carbohydrates on their surfaces that are lost during differentiation. These carbohydrates are composed of alternating galactose and N-acetylglucosamine residues and have either linear or branched architectures. Compared to the glycans expressed by many differentiated cells these glycans are poorly sialylated. However, metabolic studies reveal that there is a transient expression of sialylated glycans during the processing of glycoproteins by embryonal carcinomas. After a short pulse with mannose the major complex-type glycan is a biantennary glycan with two sialic acids. During subsequent chase periods this glycan species is replaced by unsialylated glycans that have elongated branches composed of alternating galactose and N-acetylglucosamine residues.