Galactose metabolism
Galactose metabolism
Congenital error in metabolism of D-Galactose characterized by inability of anorganism to normally metabolize galactose and lactose is called as a galactose diabetesor Galactosamia.
D-Galactose is a constituent of oligosaccharides and is produced by hydrolysisof Melibiose [1], [2], [3], [4],[5], [6], [7], Raffinose [4],[6], [7], Stachyose [4], [6],[7], Allolactose [1], [8], [9],[10], [2], [4], [6], [7],Glycerol 1-alpha-D-galactoside [4], [6], [7], Melibitol [4], [5], [6], [7], Galactinol [4], [5], [6], [7] by Galactosidase, alpha ( AGAL ), or by hydrolysis of Lactose byLactase ( LPH ) [11], [12], [13], [14]. [15].
Alpha-(D)-Galactose 1-phosphate if formed by transfer of the phosphate moietyfrom ATP to D-Galactose catalyzed by Galactokinase 2 ( GALK2 ) [16], [17], [18], [19] and Galactokinase 1 (GALK1 ) [20], [17], [21], [22],[23], [19].
Subsequent transformation of the alpha-(D)-Galactose 1-phosphate toalpha-D-Glucose 1-phosphate and UDP-D-galactose is catalyzed byGalactose-1-phosphate uridylyltransferase ( GALT ) [24], [25], [26], [27], [28], [29]. Bothproducts participate in the further transformations. Phosphoglucomutase 1 ( PGMU )then catalyzes formation of the alpha-(D)-Glucose-6-phosphate fromalpha-D-Glucose 1-phosphate [30], [31], [32],[33], [34]. UDP-D-galactose is transformed further in thetwo subsequent reactions. In the first reaction the formation of Lactose by groupof enzymes occurred: UDP-Gal:betaGlcNAc beta 1,4- galactosyltransferase, polypeptide 1 (Lactose synthase) [35], [36], [37], [38], [39] and by UDP-Gal:betaGlcNAc beta 1,4- galactosyltransferase,polypeptide 2 ( B4GT2 ) [40], [41], [42],[35], [43], [44], [39]. In the secondreaction UDP-D-galactose is transformed to UDP-D-glucose byUDP-galactose-4-epimerase ( GALE ) [45], [46], [29], [47], [48], [49]. UDP-D-glucoseparticipates in formation of Glycogen catalyzed by two enzymes, glycogen synthase2 (liver) ( GYS2 ) [50], [51], [52], [53] and by glycogen synthase 1 (muscle) ( GYS1 ) [54], [55], [56], [57], [51], [58], [59], [52]. Glycogen is the substrate of one more reaction offormation alpha-D-Glucose 1-phosphate catalyzed by Glycogen phosphorylase[60], [61], [62], [63], [64],[65], [66], [67].
Apha-D-Glucose 6-phosphate also participates in glycolysis and gluconeogenesis.Hydrolysis of Apha-D-Glucose 6-phosphate to D-Glucose is catalyzed byGlucose-6-phosphatase, catalytic subunit ( G6PT ) [68], [69], [70], [71]. This reaction can proceed also in theopposite direction under catalysis of other enzymes, Hexokinase 1 ( HXK1 ) [72], [73], [74], [75], [76], [77], [78], [79], Hexokinase-2 ( HXK2 ) [80],[81], [82], [83], [84], [76],Hexokinase 3 (white cell) ( HXK3 ) [85], [76], [86] and Glucokinase (hexokinase 4) ( HXK4 ) [87], [88], [89], [90], [91], [92], [93], [94], [95], [76], [96], [97].
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