Lactose synthase is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

that generates lactose from

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

and

UDP-galactose Uridine diphosphate galactose ( UDP- galactose) is an intermediate in the production of polysaccharides. It is important in nucleotide sugars metabolism, and is the substrate for the transferase B4GALT5. See also * Galactose * UDP galactose e ...

. It is classified under . It consists of N-acetyllactosamine synthase and

alpha-lactalbumin Lactalbumin, alpha-, also known as LALBA, is a protein that in humans is encoded by the ''LALBA'' gene. Overview α-Lactalbumin is a protein that regulates the production of lactose in the milk of almost all mammalian species. In primates, alp ...

. Alpha-lactalbumin, which is expressed in response to

prolactin Prolactin (PRL), also known as lactotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secreted from the pit ...

, increases the affinity of N-acetyllactosamine synthase for its substrate, causing increased production of lactose during lactation. N-acetyllactosamine synthase falls under the category of beta-1,4-galactosyltransferase, a type-II membrane protein found in the Golgi. Alpha-lactalbumin is a Ca²⁺ binding protein specific to mammary glands. Beta-1,4-galactosyltransferase consists of the catalytic component and alpha-lactalbumin consists of the regulatory component of lactose synthase. Alpha-lactalbumin promotes glucose binding to beta-1,4-galactosyltransferase. The beta-1,4-galactosyltransferase catalytic component consists of two flexible loops: small loop and large loop. The small loop consists of a Trp residue (Trp314) with surrounding glycine residues, meanwhile the large loop makes up amino acid residues 345 to 365. The Trp residue in the small loop moves allowing for the sugar nucleotide to be locked into the binding site. This causes a conformational change in the large loop which then creates sites for oligosaccharide and metal ion binding, and protein-protein interactions for alpha-lactalbumin.

References

External links

* EC 2.4.1 {{biochem-stub