Asialofetuin sialyltransferase from Triton X‐100 extracts of rat liver was resolved by phosphocellulose chromatography into two fractions, designated I and II in order of elution. When previously treated with Arthrobacter ureafaciens neuraminidase, fraction I eluted at about the same position as II while no alteration occurred in II. Primary rat hepatomas contained only a single asialofetuin sialyltransferase, identical to fraction I in chromatographic behavior. Transferases I and II were purified to near homogeneity. Transferase II, as well as neuraminidase‐treated I, could be sialylated auto‐catalytically, indicating that the lack of sialic acid in II is not due to the lack of a sialic‐acid‐accepting site. Both enzymes formed an (α2→6)sialylgalactoside linkage with asialo‐glycoproteins of the glycosylamine‐type and with lactose, and were indistinguishable immunologically. Nevertheless, the transferases exhibited different molecular weights of 37000 (I) and 43000 (II). When heated at 50°C, transferase I lost half its original activity within 20 min while II was scarcely inactivated. Kinetically, transferase I showed three‐times higher affinity than II for CMP‐ N ‐acetylneuraminic acid and for desialylated plasma membrane. Asialofetuin sialyltransferase was also purified from primary rat hepatoma. The purified enzyme was identical to transferase I in every respect examined. We conclude that hepatomas contain transferase I but lack transferase II.
No takes yet. Share an insight, caveat, or question.
Miyagi et al. (1982) studied this question.