期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1976
卷号：73
期号：3
页码：837-841
DOI：10.1073/pnas.73.3.837
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Incubation of mouse thymocytes with mitogenic concentrations of concanavalin A causes a 2-fold increase in cell-surface-associated (but not total cell) sialyltransferase activity (ectosialyltransferase, CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1 ) as judged by incorporation of [14C]sialic acid into endogenous cell acceptors and into added desialylated fetuin acceptor. The concanavalin-A-induced enhancement of enzymic activity is essentially complete within 1 hr after addition of mitogen and remains at elevated levels for 12 hr, declining rapidly thereafter. Intact cells labeled previously with [14C]sialic acid and then incubated briefly with hydrolytic enzymes, including neuraminidase and insoluble trypsin, released 43-66% of total cell-associated radioactivity without appreciably changing cell viability. Alterations in sialyltransferase activity due to concanavalin A treatment could not be explained by a mitogen-mediated (a) uptake of radioactive precursors, (b) cell death, (c) increased product catabolism, or (d) activation of sialyltransferase by mitogen binding to the enzyme. Furthermore, the process does not require active protein synthesis. The results are consistent with a rapid concanavalin-A-induced exposure of potential enzymic activity that was previously inaccessible to substrate.
