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Heterogeneity of human milk β(1-4) D galactosyltransferase

par Prieels, Jean-Paul ;Maes, Emmanuel;Dolmans, Marcel ;Leonis, José
Référence European journal of biochemistry / FEBS, 60, 2, page (525-531)
Publication Publié, 1975

Article révisé par les pairs

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Résumé :

β(1-4) Galactosyltransferase from human milk (the A protein of lactose synthase) has been found to be heterogeneous when fractionated by affinity chromatography against insolubilized α lactalbumin, using a linear gradient of decreasing N acetylglucosamine concentration. Three forms were isolated. Molecular weights of the different species, as determined by sodium dodecylsulphate gel electrophoresis, were found to be 38000, 43000 and 50000. The 38000 and 50000 species were studied for their catalytic ability to synthesize either lactose in the presence of α lactalbumin, or N acetyllactosamine in the presence and absence of the 'specifier' protein. Appreciable difference was observed between the two enzyme forms with respect to their catalysis of lactose synthesis with α lactalbumins from various sources. Differences in the rate of production of N acetyllactosamine in the presence of α lactalbumin were also observed. For the lowest molecular weight species it was found that the inhibitory effect of α lactalbumin upon N acetyllactosamine synthesis becomes an activating effect at higher α lactalbumin concentrations, while no such inversion was observed for the other species. The results suggest that the conformation at the site of association of the enzyme with the acceptor saccharide or α lactalbumin has been changed, presumably by a partial enzymic hydrolysis.