alpha -Lactalbumin (LA) Stimulates Milk beta-1,4-Galactosyltransferase I (beta 4Gal-T1) to Transfer Glucose from UDP-glucose to N-Acetylglucosamine: CRYSTAL STRUCTURE OF beta 4Gal-T1·LA COMPLEX WITH UDP-Glc*

  • Ramakrishnan, Boopathy
  • Shah, Premal S.
  • Qasba, Pradman K.
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Publication date
October 2001
Publisher
American Society for Biochemistry & Molecular Biology (ASBMB)

Abstract

beta-1,4-Galactosyltransferase 1 (Gal-T1) transfers galactose (Gal) from UDP-Gal to N-acetylglucosamine (GlcNAc), which constitutes its normal galactosyltransferase (Gal-T) activity. In the presence of alpha -lactalbumin (LA), it transfers Gal to Glc, which is its lactose synthase (LS) activity. It also transfers glucose (Glc) from UDP-Glc to GlcNAc, constituting the glucosyltransferase (Glc-T) activity, albeit at an efficiency of only 0.3-0.4% of Gal-T activity. In the present study, we show that LA increases this activity almost 30-fold. It also enhances the Glc-T activity toward various N-acyl substituted glucosamine acceptors. Steady state kinetic studies of Glc-T reaction show that the Km for the donor and acceptor substrates are high ...

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