E. Meezan et al., XYLOSYL TRANSFER TO AN ENDOGENOUS RENAL ACCEPTOR - CHARACTERISTICS OFTHE REACTION AND PROPERTIES OF THE PRODUCT, The Journal of biological chemistry, 269(15), 1994, pp. 11503-11508
In the course of a study of UDP-xylose:proteoglycan core protein xylos
yltransferase (EC 2.4.2.26), another xylosyltransferase was discovered
in the soluble fraction of a rat kidney homogenate. The latter enzyme
catalyzed [H-3]xylosyl transfer from UDP-[H-3]xylose to an endogenous
acceptor and yielded a product in which the xylose was bound by an al
kali-stable linkage. It was therefore concluded that the acceptor was
not the core protein of one of the proteoglycans containing a xylose -
-> serine linkage, since this linkage is cleaved by alkali. The [H-3]x
ylose-labeled product emerged with the void volume when chromatographe
d on Sephadex G-50, it was precipitated by trichloroacetic acid, and i
t had a mobility on sodium dodecyl sulfate-polyacrylamide gel electrop
horesis corresponding to a molecular mass of about 32,000 Da. Digestio
n with trypsin or alpha-amylase degraded the labeled product to small
fragments, as determined by gel chromatography, suggesting that it was
a glycoprotein related to glycogen. A product of similar characterist
ics was formed when UDP-[H-3]glucose was substituted for UDP-[H-3]xylo
se as the glycosyl donor, and the two nucleotide sugars were mutually
competitive in the respective transfer reactions, indicating that they
were substrates for the same enzyme. On the basis of these findings,
it was tentatively concluded that the xylosyltransferase and its accep
tor were the renal form of glycogenin.