STUDIES ON THE BIOSYNTHESIS OF GLYCO-SPHINGOLIPIDS IN CULTURED MOUSE NEUROBLASTOMA CELLS: CHARACTERIZATION AND ACCEPTOR SPECIFICITIES OF N-ACETYLNEURAMINYL- AND N-ACETYLGALACTOSAMINYLTRANSFERASES |
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Authors: | S F Kemp A C Stoolmiller |
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Institution: | Departments of Pediatrics and Biochemistry and the Joseph P. Kennedy, Jr. Mental Retardation Research Center, University of Chicago, Chicago, IL 60637, U.S.A. |
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Abstract: | Abstract— The pathway of biosynthesis of N -acetylgalactosamine-containing gangliosides in mouse neuroblastoma has been studied using NB41A cells grown in monolayer tissue culture. Cell-free enzyme preparations catalyzed the transfer of NeuNAc from CMP-NeuNAc to lactosylceramide (GL-2a), to form GM3. Asialo-GM2 was neither an acceptor nor a competitive inhibitor of the sialyltransferase (CMP-NeuNAc: GL-2a N-acetylneuraminyltransferase, EC 2.4.99.-) under a variety of experimental conditions. Enzyme preparations also contained an N -acetylgalactosaminyltransferase (UDP-GalNAc. GM3 N -acetylgalactosaminyltransferase, EC 2.4.1.-) which catalyzed the conversion of GM3 to GM2. No significant transfer of N -acetylgalactosamine to GL-2a could be demonstrated. The results of the glycosyltransferase assays support the concept that the first NeuNAc of brain gangliosides is introduced into GL-2a. The present data suggests that the occurrence of asialo-GM2 in NB41A cells under some culture conditions is a consequence of the catabolism of higher gangliosides. |
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