Glycosyltransferase activity

Many different glycosyltransferase activities involved in higher plant wall biosynthesis have been identified in cell free membrane fractions, but in only a few cases has glycosyltransferase activity been retained in detergent-solubilized preparations, and in even fewer cases have any purified polypeptides been identified as plant cell wall glycosyltransferases (29,33). 

Borisova, S., Zhao, L., Melancon, C.E. et al. (2004) Characterization of the glycosyltransferase activity of desVII analysis of and implications for the biosynthesis of macrolide antibiotics. Journal of the American Chemical... 

Myllyla and coworkers produced three different mouse lines with a manipulated LH3 gene. The mouse line (LH mutant) with a point mutation that specifically destroys the LH activity of LH3 without affecting glycosyltransferase activities was viable. A complete loss of LH3 causes early embryonic lethality in mice. ... 

The present review covers a description of methodology and properties of UDP-glucuronyltransferase and of related UDP-glycosyltransferase activities (assayed with bilirubin as the acceptor substrate) and attempts to delineate applications to human disease. Studies with other hydro-phobic acceptor substances will be discussed as far as relevant to the subject matter. 

Obviously, extrapolation procedures are impractical for routine determination of enzyme activities. When substrate saturation-curves conform to rectangular hyperbolas, reasonable concentrations of substrates should equal 10 to 20 times the respective Km values. As outlined above, application of this rule to assays of bilirubin UDP-glycosyltransferase activities is hampered by substrate inhibition and by occasional deviation from Michaelis-Menten kinetics. The best alternative in such cases may be to choose the concentrations at optimal enzyme activity. However, great care should be exercised in interpreting the results. When a bio-... 

Partial or total deficiency, or inhibition of bilirubin UDP-glucuronyltransferase may cause unconjugated hyperbilirubinemia. Increased production (hemolysis, ineffective erythropoiesis) should be excluded by investigating hematologic parameters. Determination in vitro of bilirubin UDP-glycosyltransferase activities can contribute to a differential diagnosis. To minimize the effect of cytoplasmic carrier proteins, in in vitro... 

Based on data cited previously it appears that TPA s primary effect is at the cell surface (55, 56). This does not exclude the possibility that TPA is transported and metabolized to an "active" intermediate, which then affects glycosyltransferase activity. However, it is possible (particularly in light of the structural dissimilarity between TPA and RA) that these compounds affect glycoconjugate metabolism in different ways. 

Although these results are difficult to interpret in molecular terms, they provide a basis for further research. The morphological changes brought about from these mixing experiments suggest that the TPA-induced increases in glycosyltransferase activity are the result of a different process than those induced by RA or butyrate (manuscript in preparation). 

N4TG1 cells were exposed to drugs for 8 hrs. and the homogenates assayed for glycosyltransferase activity as described in the text... 

Schwartz B, Markwalder JA, Seitz SP, Wang Y, Stein RL. A kinetic characterization of the glycosyltransferase activity of Eschericia coli PBP lb and development of a continuous fluorescence assay. Biochemistry 2002 41 12552-12561. 

Kuiipers, T W, Terminal glycosyltransferase activity a selective role in cell adhesion. Blood, 81, 873-882, 1993. 

In animal tissues, glycolipids are important constituents of the plasma membrane. They play a significant role in cell-cell communications, cellular differentiation, and proliferation, and also in oncogenesis, as indicated by alterations in their compositions and in glycosyltransferase activities during differentiation and growth of cells. 

After the glycosyltransferase of interest has been pmchased or isolated, it is desirable to verify the activity of the enzyme with a standard substrate and the compound of interest under the conditions of the preparative synthesis. Methods for assaying glycosyltransferase activity are summarized in Table 1, and a suitable method should be selected based on the characteristics of the substrate and the required sensitivity of the assay. Kinetic studies to obtain Km and Kiax values for the substrate and optimization of reaction conditions, including buffer and pH, should also be carried out. 

At least, these findings create a field for the hypothesis, that carbohydrate structures could be used as a specific taxonomic marker. However further confirmation should come through the study of other species. The data also point to the diversity of novel glycosyltransferase activities which remain to be studied with regard to animal evolution. 

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