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The binding of glycoconjugates to human milk D galactosyltransferase

par Prieels, Jean-Paul ;Dolmans, Marcel ;Schindler, Melvin;Sharon, Nathan
Référence European journal of biochemistry / FEBS, 66, 3, page (579-582)
Publication Publié, 1976

Article révisé par les pairs

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Résumé :

Through the use of affinity chromatography, a homogeneous preparation of human β(1→4) D glactosyltransferase (the A protein of lactose synthase) was obtained. The specificity of this protein for glycoconjugates was studied in the presence and absence of human α lactalbumin. A kinetic analysis of the transfer of D galactose to N acetyl D glucosamine and to β(1→4) linked N acetylglucosamine oligomers, suggested that the active site region of the enzyme contains more than one binding site for acceptor molecules. Furthermore, experiments with N acetylglucosamine β(1→4) N acetylmuramic pentapeptide isolated from Micrococcus luteus indicated that the presence of a peptide chain does not enhance enzymic activity, as compared with the corresponding free disaccharide. Similar results were obtained using ovalbumin and the ovalbumin glycopeptide (which have similar apparent K(m) values for A protein) as galactose acceptors. In contrast to its ability to inhibit N acetyllactosamine production, α lactalbumin did not inhibit the transfer of D galactase to the N acetylglucosamine oligomers or the glycopeptides. Although α lactalbumin can switch the specificity of A protein from N acetyl D glucosamine to D glucose resulting in the production of lactose, no transfer of galactose was observed to β(1→4) linked glucose oligomers or to a collagen glycopeptide, D glucopyranosyl α(1→2) D galactopyranosyloxy β(1→5) lysine. It therefore appears that α lactalbumin can only modify human A protein for monosaccharide acceptors.