Structure-function relationships in lactose synthase. Structural requirements of the uridine 5'-diphosphate galactose binding site

Biochemistry. 1982 Dec 7;21(25):6340-3. doi: 10.1021/bi00268a003.

Abstract

The structural requirements for the donor pyranosyl moiety of UDP-Gal in either galactosyl transfer or "lactose" biosynthesis have been determined. The 4"-deoxy analogue, UDP-4"-deoxyglucose, was synthesized and fully characterized as a donor substrate for galactosyltransferase. The relative rate of deoxyglucosyl transfer to glucose or GlcNAc acceptors was 5.5 +/- 0.6% of that of UDP-Gal as the substrate, with Km values in the same range as that for UDP-Gal or UDP-Glc. Several conclusions may be drawn as to the detailed structural requirements of the UDP-Gal binding site: an axial 4"-hydroxyl group on the pyranosyl moiety is necessary for precise substrate alignment as is also an equatorial 6"-CH2OH moiety. Where one or the other moiety was lacking (UDP-dGlc or UDP-Arab), the maximal rate of glycosyl transfer was ca. 1/20th that of UDP-Gal.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Binding Sites
  • Deoxyglucose / metabolism
  • Kinetics
  • Lactose Synthase / metabolism*
  • Structure-Activity Relationship
  • Uridine Diphosphate Galactose / metabolism*
  • Uridine Diphosphate Sugars / metabolism*

Substances

  • Uridine Diphosphate Sugars
  • Uridine Diphosphate Galactose
  • Deoxyglucose
  • Lactose Synthase