Biological and biochemical properties of two Xenopus laevis N-acetylgalactosaminyltransferases with contrasting roles in embryogenesis.
Bottom Line: Until now, the mammalian forms of these enzymes have been the best characterized.In terms of enzymatic activity, both enzymes were found to be active towards the EA2 peptide, but display differential activity towards a peptide based on the sequence of ActR-IIB, a receptor relevant to TGF-β/BMP signaling.In summary, these data demonstrate that these two enzymes from different branches of the N-acetylgalactosaminyltransferase do not only display differential substrate specificities, but also specific and distinct expression pattern and biological activities in vivo.
Affiliation: Department für Chemie, Universität für Bodenkultur, Wien, Austria; Manchester Interdisciplinary Biocentre, University of Manchester, UK.Show MeSH
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Mentions: Performing the reaction at different temperatures (16, 22, 30, 37, 42, 48 and 55 °C) with the optimized conditions described above showed that both enzymes had their maximum activity at 42 °C (Fig. 4a). Relatively few data have seemingly been published on the temperature optimum of other recombinant N-acetylgalactosaminyltransferases; isoforms from Caenorhabditis were most active at 23 °C (Hagen and Nehrke, 1998), similar to data on cestode and fly enzymes (Echinococcus GalNAc-T1 at 28 °C and Drosophila GalNAc-T3 at 29–33 °C) (Freire et al., 2004; Nakamura et al., 2004). The comparison with the temperature optima of other glycosyltransferases (e.g., the peptide O-xylosyltransferases) suggests that frog enzymes might have a higher temperature optimum than for mammalian or invertebrate enzymes (Brunner et al., 2006; Voglmeir et al., 2007). The reason for this elevated temperature maximum could be that frogs are like all other amphibians ectotherm, and have therefore to adjust their body temperature also to many different surroundings (Feder and Burggren, 1992). Although both isoforms reach maximum activity at a temperature of 42 °C, xGalNAc-T6 seems to have a slightly lower optimum than xGalNAcT-16, judged by the lower activity of the enzyme at 48 °C. However, due to reduced stability at higher temperatures as observed in preliminary experiments, the incubation temperature for other experiments was kept at 37 °C.
Affiliation: Department für Chemie, Universität für Bodenkultur, Wien, Austria; Manchester Interdisciplinary Biocentre, University of Manchester, UK.