Transfer reactions 0-galactosidase

The concentration of acceptor was varied between 0.1 and 5.0 M. The concentration of water ( 55 M) was always very high in comparison to that of the a( ( cptor. Occurrence of a transfer reaction under these conditions shows that the organic acceptors have a higher affinity for the enzyme than for water.(Compare the results with /3-galactosidases.)... 

Maltase and a-glucosidases in general catalyze transfer reactions in the same manner as galactosidases. It was shown many years ago that maltose hydrolysis could be reversed, although the structure of the product was not established conclusively. Experiments with maltose and labeled glucose have shown the incorporation of the isotope into maltose during incubation with an enzyme preparation from intestinal mucosa.i ... 

The reaction time of a transglycosylation may also be an important determinant of the product outcome. For example, the (1-4) linked disaccharide (A A -diacetylchitobiose) was the initial product formed when a mixture of A-acetyl-D-glucosamine and p-nitrophenyl (3-d-2-A-acetyl glucosamide was treated with p-galactosidase from Aspergillus oryzae (Scheme 4.26).76 The only other transfer product observed was the corresponding (1-6) linked disaccharide formed at 10% of the total... 

In order to characterize the extent of transgalactosylation in a )3-galactosidase-catalyzed reaction, Wallenfels et al. [20] defined the transfer number (Y) as follows ... 

Ariga et al. [48] have investigated the behavior of the monolith reactor in which Echerichia coli with P-galactosidase or Saccharomyces cerevisiae was immobilized within a thin film of K-carragcenan gel deposited on the channel wall. The effects of mass transfer resistance and axial dispersion on the conversion were studied. Those authors found that the monolith reactor behaved like the plug-flow reactor. The residence-time distribution in this reactor was comparable to four ideally mixed tanks in series. The influence of gas evolution on liquid film resistance in the monolith reactor was also investigated. It was shown that at low superficial gas velocities, the gas bubble may adhere to the wall, which decreases the effective surface area available for the reaction. The authors concluded that the reactor was very effective in the reaction systems accompanied by gas evolution, such as fermentations. 

A -galactosidase of Bacillus circulans can transfer a jS-D-galactopyranosyl residue of lactose to A-acetylglucosamine according to reaction (10.17). 

All six enzymes, substrates and cofactors are mixed together to achieve a one-pot reaction. The pH adopted, 7.5, is suitable for all enzymes involved in sialylation, but far from the optimal pH for the galactosidase which is 4.3. However, the reaction could be conducted at pH 7.5 because galactosyl transfer to GalNAc is an efficient process and transglycosidation in synthesis is quite often more... 

The transfer galactosylation with /3-galactosidase from Bacillus circulans for the synthesis of N-acetyllactosamine starting from lactose and N-acetylglucosamine [44] has been studied. When performing the reaction in an aqueous system the problem of this approach lies in the secondary hydrolysis of the product by the same enzyme. As a consequence, yields are less than 30%, and it is important to separate enzyme and product when the maximum yield is obtained. By addition of 25% v/v of [MMIM][MeS04] as a water-miscible co-solvent the water activity of the medium is decreased and, consequently, the secondary hydrolysis of the... 

The j8-galactosidase from the Pencillium simplicissimum isolated from soil has high galactosyltransferase activity Synthesis of galactoohgosaccharides from 3 to 4 units of monosaccharide. When monosaccharides are present in the reaction system, the transfer activity of the enzyme will be inhibited, so only by the enzyme from P. simplicissimum cultured under the non-optimum hydrolysis conditions, galactooligosaccharide production can reach the maximum. For example, the lactose solution (concentration of 60%) incubated at pH 6.5 and 50 C obtained the maximum conversion rate. The product composition was 30.5% galacto-ohgosaccharide, 27.5% residual lactose and 42% free monosaccharides. 

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