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Galactose (/ ɡ ə ˈ l æ k t oʊ s /, galacto-+ -ose, "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. [2] It is an aldohexose and a C-4 epimer of glucose. [3] A galactose molecule linked with a glucose molecule forms a lactose molecule.
Galactokinase is an enzyme (phosphotransferase) that facilitates the phosphorylation of α-D-galactose to galactose 1-phosphate at the expense of one molecule of ATP. [1] Galactokinase catalyzes the second step of the Leloir pathway , a metabolic pathway found in most organisms for the catabolism of α-D-galactose to glucose 1-phosphate . [ 2 ]
In humans it is the terminal carbohydrate forming the antigen of blood group A. [1]. It is typically the first monosaccharide that connects serine or threonine in particular forms of protein O-glycosylation.
Galactosemia, the inability to metabolize galactose in liver cells, is the most common monogenic disorder of carbohydrate metabolism, affecting 1 in every 55,000 newborns. [2] When galactose in the body is not broken down, it accumulates in tissues. The most common signs are failure to thrive, hepatic insufficiency, cataracts and developmental ...
GalT encodes for the protein galactosyltransferase which catalyzes the transfer of a galactose sugar to an acceptor, forming a glycosidic bond. [5] GalK encodes for a kinase that phosphorylates α-D-galactose to galactose 1-phosphate. [6] Lastly, galM catalyzes the conversion of β-D-galactose to α-D-galactose as the first step in galactose ...
Accumulated galactose can also undergo an alternative reaction: Oxidation to galactonate. The mechanism of galactonate formation is still unclear. However, recent studies suggest that galactose dehydrogenase is responsible for converting galactose to galactonolactone, which then spontaneously or enzymatically converts to galactonate. Once ...
Intermediates and enzymes in the Leloir pathway of galactose metabolism [5] In the first step, galactose mutarotase facilitates the conversion of β-D-galactose to α-D-galactose since this is the active form in the pathway. Next, α-D-galactose is phosphorylated by galactokinase to galactose 1-phosphate.
GALT catalyzes the second reaction of the Leloir pathway of galactose metabolism through ping pong bi-bi kinetics with a double displacement mechanism. [6] This means that the net reaction consists of two reactants and two products (see the reaction above) and it proceeds by the following mechanism: the enzyme reacts with one substrate to generate one product and a modified enzyme, which goes ...