Differential effect of alpha-lactalbumin on beta-1,4-galactosyltransferase IV activities.
We isolated a human cDNA clone encoding beta-1,4-galactosyltransferase (beta-1,4-GalT IV) which shares 37% identity with previously characterized mammalian beta-1,4-GalT (beta-1,4-GalT I). By transfection of the full length cDNA into Sf-9 cells and assay of the cell homogenates, higher beta-1,4-GalT activity toward GlcNAc beta-S-pNP was obtained, and its activity was modulated with alpha-lactalbumin, while no lactose synthetase activity was detected in the presence of alpha-lactalbumin. Northern blot analysis using total and poly (A)+ RNA preparations revealed that the expression level of beta-1,4-GalT IV transcript is low and relatively constant while that of beta-1,4-GalT I transcript is dramatically increased in the mouse mammary gland during lactation. These results indicate that beta-1,4-GalT IV can interact with alpha-lactalbumin but has no lactose synthetase activity.
Sato
T
T
Department of Biosignal Research, Tokyo Metropolitan Institute of Gerontology, Japan.
Aoki
N
N
Matsuda
T
T
Furukawa
K
K
D000818:Animals; D005260:Female; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D007768:Lactalbumin / Q000378:metabolism*; D007774:Lactation / Q000378:metabolism*; D007785:Lactose / Q000096:biosynthesis; D007788:Lactose Synthase / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000201:enzymology*; D051379:Mice; D011485:Protein Binding; D012333:RNA, Messenger / Q000032:analysis; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
D006023:Glycoproteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D007768:Lactalbumin; D005700:Galactosyltransferases; C111678:beta-1,4-galactosyltransferase IV; D007788:Lactose Synthase; D007785:Lactose