Galactosyl transfer

It has been suggested that a similar mechanism of D-galactosyl transfer may be involved in the biosynthesis of galactomannan, with the participation of GDP-D-mannose.143,146 Courtois and coworkers145 have, in fact, detected UDP-D-galactose and GDP-D-mannose in fenugreek seeds. 

Enzymatic galactosyl transfer from UDP-Gal to the 4-position of GIcNAc catalyzed by /J1-4 galactosyltransferase (/31,4-GalT)... 

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... 

Analyses of deuterium and oxygen-18 kinetic isotope effects provide evidence of the form, abundance, and galactosyl transfer mechanism related to intermediates. 

H19. Helting, T., and Rod6n, L., Biosynthesis of chondroitin sulfate. I. Galactosyl transfer in the formation of the carbohydrate-protein linkage region. J. Bid. Chem. 244, 2790-2798 (1969). 

Galactosylceramide can act as an acceptor for a further galactosyl transfer from UDPGal in kidney, to form the lipid Galal,4Gaipi-l Cer (or Gl-2b), which is found in human kidney and brain, lungs of pigs and in the thymus. In mice it appears only in the kidney of certain strains (e.g. Balb/c). 

The likely sulphate donor for all of these glycolipids is phosphoadenosyl phosphosulphate (adenosine 3 -phosphate 5 -phosphosulphate), which is known to be the physiological donor for Gl-lbS. In the synthesis of GL-lbS sulphate transfer and galactosyl transfer are coupled it is probable that different sulphotransferases act in producing the other sulphoglycolipids. 

Kfen, V., Auge, C, Sedmera, P. and Havlicek V. (1994b) -Glucosyl and -galactosyl transfer catalysed by fS-1, 4-galactosyltransferase in preparation of glycosylated alkaloids./. Chem. Soc. Perkin Trans. 1, 2481-2484. 

The product of galactosyl transfer was characterized by the isolation, following alkaline hydrolysis, of a radioactive compound, which had the same migration characteristics upon Dowex 50 chromatography and paper electrophoresis as did galactosylhydroxylysine. After acid hydrolysis of the labeled compound, only galactose and hydroxylysine were detected, and all the radioactivity resided with galactose. 

These findings (Eylar and Cook, 1965 Caccam and Eylar, 1970 Molnar et al., 1969c) indicate that galactosyl transfer occurs predominantly on a smooth-surfaced fraction distinct from smooth endoplasmic reticulum the identity of this fraction as either Golgi apparatus or plasma membrane remains to be established. Hexosamine and mannose incorporation, however, probably occurs on both rough and smooth membranes. This pattern of sugar incorporation is similar to that described for liver and other tissues (see previous sections). 

The use of endogenous acceptor is obviously not ideal for a study of the properties of the tw O galactosyl transfer reactions, and in view of the modest yields of products labeled in the second galactose position, further studies with exogenous substrates were undertaken. This permitted the... 

The product of the reaction was 4-0-jS-D-galactosyl-D-xylose, as could be expected from the known structure of the linkage region. Table II summarizes the results obtained with a number of exogenous acceptors, and it is seen that 0- 8-D-xylosy -L-serine Mas approximately twice as good a substrate as xylose. However, the ready availability of the latter obviously makes it the substrate of choice for the assay of the first galactosyl transfer step. 

---