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 characte rized mammalian beta-1,4-GalT (beta-1,4-GalT l). By transfection of th e 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, a nd 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 l ow and relatively constant while that of beta-1,4-GalT l transcript is dramatically increased in the mouse mammary gland during lactation. T hese results indicate that beta-1,4-GalT IV can interact with alpha-la ctalbumin but has no lactose synthetase activity. (C) 1998 Academic Pr ess.