Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

When homogenates of rat liver and hepatomas were centrifuged at 78 000 X g, over 90% of liver N-acetylglucosaminyltransferase assayed with beta-galactosidase- and beta-N-acetylhexosaminidase-treated asialofetuin as acceptor was recovered in the particulate fraction, while as much as 24% of hepatoma transferase was in the supernatant fraction. The particulate transferase solubilized by 0.2% sodium deoxycholate emerged from a DEAE-cellulose column at 0.04 M NaCl (transferase A). The supernatant fractions from all the hepatomas tested contained a second N-acetylglucosaminyltransferase eluted from the column at 0.02 M NaCl (transferase B). Transferase B was absent from liver supernatant fraction. The activities of these transferases toward various acceptors and the effect of beta-N-acetylhexosaminidase on their products suggest that both transferases are UDP-N-acetylglucosamine : alpha-mannoside beta-N-acetylglucosaminyltransferase. Although ovalbumin and glycopeptide V, which was isolated from pronase digest of ovalbumin, were good acceptors, transferase A utilized ovalbumin and glycopeptide V with apparent Km values of 0.44 and 0.33 mM, respectively, whereas the corresponding values for transferase B were 4.5 and 0.050 mM.
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PMID:Studies on UDP-N-acetylglucosamine : alpha-mannoside beta-N-acetylglucosaminyltransferase of rat liver and hepatomas. 617 Mar 35

Inflammation results in an increase in the levels of a variety of glycoproteins in serum. The glycoproteins that respond in this way are usually referred to as acute-phase reactants. Studies on the acute-phase response of rat alpha 1-acid glycoprotein showed that there was an increase in the liver levels of this glycoprotein at 12 h after turpentine inflammation. This was followed by increased serum levels at 48-72 h after inflammation, suggesting a precursor-product relationship between liver and serum alpha 1-acid glycoprotein. Incorporation studies coupled with measurements of synthesis rates of alpha 1-acid glycoprotein showed that increased synthesis was responsible for the acute-phase response of this protein to inflammation. These studies also showed that albumin was a negative acute-phase reactant. The acute-phase response of alpha 1-acid glycoprotein was accompanied by increased liver pools of UDP-N-acetylglucosamine (UDP-GlcNAc) and UDP-N-acetylgalactosamine (UDP-GalNAc) and increased liver activities of glucosamine-6-phosphate synthase and UDP-GlcNAc 2-epimerase. Activities of galactosyl and sialyl transferases in liver were also elevated and serum sialyl transferase was increased substantially in inflammation, suggesting that it may also be an acute-phase reactant. Liver activities of beta-N-acetylhexosaminidase and beta-galactosidase declined by about 50% at 24 h after inflammation; there was evidence that serum levels of these enzymes increased at 24-72 h after inflammation, suggesting that the lysosomal glycosidases may be released from liver during inflammation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Glycoprotein biosynthesis during the acute-phase response to inflammation. 662 6

The effect of ammonium on the glycosylation pattern of the recombinant immunoadhesin tumor necrosis factor-IgG (TNFR-IgG) produced by Chinese hamster ovary cells is elucidated in this study. TNFR-IgG is a chimeric IgG fusion protein bearing one N-linked glycosylation site in the Fc region and three complex-type N-glycans in the TNF-receptor portion of each monomer. The ammonium concentration of batch suspension cultures was adjusted with glutamine and/or NH(4)Cl. The amount of galactose (Gal) and N-acetylneuraminic acid (NANA) residues on TNFR-IgG correlated in a dose-dependent manner with the ammonium concentration under which the N-linked oligosaccharides were synthesized. As ammonium increased from 1 to 15 mM, a concomitant decrease of up to 40% was observed in terminal galactosylation and sialylation of the molecule. Cell culture supernatants contained measurable beta-galactosidase and sialidase activity, which increased throughout the culture. The beta-galactosidase, but not the sialidase, level was proportional to the ammonium concentration. No loss of N-glycans was observed in incubation studies using beta-galactosidase and sialidase containing cell culture supernatants, suggesting that the ammonium effect was biosynthetic and not degradative. Several biosynthetic mechanisms were investigated. Ammonium (a weak base) is known to affect the pH of acidic intracellular compartments (e.g., trans-Golgi) as well as intracellular nucleotide sugar pools (increases UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine). Ammonium might also affect the expression rates of beta1, 4-galactosyltransferase (beta1,4-GT) and alpha2,3-sialyltransferase (alpha2,3-ST). To separate these mechanisms, experiments were designed using chloroquine (changes intracellular pH) and glucosamine (increases UDP-GNAc pool [sum of UDP-GlcNAc and UDP-GalNAc]). The ammonium effect on TNFR-IgG oligosaccharide structures could be mimicked only by chloroquine, another weak base. No differences in N-glycosylation were found in the product synthesized in the presence of glucosamine. No differences in beta1, 4-galactosyltransferase (beta1,4-GT) and alpha2,3-sialyltransferase (alpha2,3-ST) messenger RNA (mRNA) and enzyme levels were observed in cells cultivated in the presence or absence of 13 mM NH(4)Cl. pH titration of endogenous CHO alpha2,3-ST and beta-1,4-GT revealed a sharp optimum at pH 6.5, the reported trans-Golgi pH. Thus, at pH 7.0 to 7.2, a likely trans-Golgi pH range in the presence of 10 to 15 mM ammonium, activities for both enzymes are reduced to 50% to 60%. Consequently, ammonium seems to alter the carbohydrate biosynthesis of TNFR-IgG by a pH-mediated effect on glycosyltransferase activity.
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PMID:Ammonium alters N-glycan structures of recombinant TNFR-IgG: degradative versus biosynthetic mechanisms. 1079 88

The second step of dolichol-linked oligosaccharide synthesis in the N-linked glycosylation pathway at the endoplasmic reticulum (ER) membrane is catalyzed by an unusual hetero-oligomeric UDP-N-acetylglucosamine transferase that in most eukaryotes is comprised of at least two subunits, Alg13p and Alg14p. Alg13p is the cytosolic and catalytic subunit that is recruited to the ER by the membrane protein Alg14p. We show that in Saccharomyces cerevisiae, cytosolic Alg13p is very short-lived, whereas membrane-associated Alg13 is relatively stable. Cytosolic Alg13p is a target for proteasomal degradation, and the failure to degrade excess Alg13p leads to glycosylation defects. Alg13p degradation does not require ubiquitin but instead, requires a C-terminal domain whose deletion results in Alg13p stability. Conversely, appending this sequence onto normally long-lived beta-galactosidase causes it to undergo rapid degradation, demonstrating that this C-terminal domain represents a novel and autonomous degradation motif. These data lead to the model that proteasomal degradation of excess unassembled Alg13p is an important quality control mechanism that ensures proper protein complex assembly and correct N-linked glycosylation.
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PMID:Alg13p, the catalytic subunit of the endoplasmic reticulum UDP-GlcNAc glycosyltransferase, is a target for proteasomal degradation. 1833 70