XYLOSYL TRANSFER TO AN ENDOGENOUS RENAL ACCEPTOR - PURIFICATION OF THE TRANSFERASE AND THE ACCEPTOR AND THEIR IDENTIFICATION AS GLYCOGENIN

A xylosyltransferase in rat kidney, tentatively identified as glycogen in (Meezan, E., Ananth, S., Manzella, S., Campbell, P., Siegal, S., Pi llion, D. J., and Roden, L. (1994) J. Biol. Chem. 269,11503-11508), wa s purified by a procedure in which affinity chromatography on UDP-gluc uronic acid-agarose was a particularly useful step. The purified mater ial was nearly homogeneous, as shown by SDS-polyacrylamide gel electro phoresis and silver staining, and had an electrophoretic mobility corr esponding to a M(r) of 32,000. The purified enzyme possessed both gluc osyl- and xylosyltransferase activity, and incubation with UDP-[H-3]xy lose or UDP-[H-3]glucose yielded a single macromolecular product, whic h had the same electrophoretic mobility as the major silver-stained co mponent. These results indicate that the kidney transferase was indeed glycogenin and that it was functionally analogous to the larger glyco genin species previously isolated from rabbit muscle. Further examinat ion of the properties of the rat kidney enzyme showed, i.a., that it w as inhibited strongly by cytidine 5'-diphosphate. This effect was used to advantage in an alternative purification procedure, which was appl ied to beef kidney and involved adsorption of the enzyme to UDP-glucur onic acid-agarose and subsequent elution with cytidine 5'-diphosphate. In contrast to glycogenin, glycogen synthase did not catalyze transfe r from UDP-xylose, and it is suggested that the incorporation of xylos e into glycogen observed by other investigators was due to glycogenin- catalyzed xylosyl transfer and subsequent chain elongation by glycogen synthase.