Fructose and mannose metabolism - Homo sapiens (human)

Curator(s): Joe Strothman

This pathway illustrates the shared catabolic fates of both fructose and mannose. Fructose occurs naturally in foods as a free monosaccharide and as a component of the disaccharide sucrose. It is also widely used as a sweetener. In the body, fructose is converted to dihydroxyacetone phosphate and D-glyceraldehyde 3-phosphate in a sequence of three reactions. First, fructose is phosphorylated, then cleaved by aldolase to yield dihydroxyacetone phosphate and D-glyceraldehyde, which is phosphorylated to yield D-glyceraldehyde 3-phosphate. The cleavage of fructose 1-phosphate is catalyzed by the same enzyme that catalyzes the reversible cleavage of fructose 1,6-bisphosphate in glycolysis. The isoform of this enzyme found in liver, kidney, and intestine (B) is approximately equally active with fructose 1-phosphate and fructose 1,6-bisphosphate as substrates, while the muscle and brain isoforms (A and C, respectively), have little activity with fructose 1-phosphate. Fructose metabolism thus occurs mainly in tissues expressing the B isoform. Compared to fructose, mannose is not well metabolized in humans and it does not significantly enter most carbohydrate metabolism pathways when taken orally. Indeed it appears that 90% of mannose ingested is excreted unconverted into the urine within 30 – 60 minutes, with 99% of the remainder being excreted within the following 8 hours. On the other hand, mannose is present in numerous glycoconjugates including N-linked glycosylated proteins. What little mannose is metabolized appears to be phosphorylated and either converted to GDP mannose and sent on to N-glycan biosynthesis or it is isomerized by mannose-6-phosphate isomerase into beta-fructose-6-phosphate, which then can be directed into the fructose catabolic pathway. [PathMap]


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Fructose and mannose metabolism - Homo sapiens (human) node1 node3 D-Sorbitol node1->node3 node2 L-Sorbose node2->node1 node13 node2->node13 node3->node13 node4 Alpha -D -Glucose Galactose metabolism node4->Galactose metabolism node5 D-Mannitol node5->node13 node17 node5->node17 node6 D-Mannitol -1P node7 node7->node3 node7->node4 node8 node8->node3 node14 D-Fructose node8->node14 node9 node9->node3 node9->node14 node10 node10->node4 node10->node14 node11 D-Fructose -1P node12 node12->node11 node13->node6 node13->node11 node29 D-Mannose -6P node13->node29 node41 D-Sorbitol -6P node13->node41 node42 L-Sorbose -1P node13->node42 node14->node12 node14->node13 node26 node14->node26 node27 node14->node27 node15 node15->node14 node16 3.1.3.- node16->node14 node17->node14 node18 node18->node5 node18->node14 node19 node19->node5 node19->node14 node20 D-Fructose -2P node20->node16 node21 node21->node5 node21->node14 node22 node22->node5 node22->node6 node23 node23->node6 node31 Beta -D -Fructose-6P node23->node31 node24 node24->node20 node25 3 node26->node25 node26->node29 node26->node31 node27->node31 node28 node28->node29 node30 D-Mannose node30->node13 node30->node26 node30->node28 node114 Amino sugar and nucleotide sugar metabolism - Homo sapiens (human) node30->node114 node34 node31->node34 node39 node31->node39 node32 D-Fructose -2,6P2 node32->node24 node33 node32->node33 node33->node31 node34->node32 node35 node35->node29 node35->node31 node36 node36->node31 node37 node37->node31 node56 Beta -D -Fructose-1,6P2 node37->node56 node38 2 node39->node38 node39->node56 node40 node40->node31 node40->node41 node43 ADP-mannose node44 node43->node44 node45 D-Mannose -1P node44->node45 node46 node45->node46 node47 node45->node47 node48 GDP -D -mannose node46->node48 node47->node48 node48->node44 node50 2.4.1.- node48->node50 node59 node48->node59 node62 node48->node62 node69 node48->node69 node115 N-Glycan biosynthesis node48->node115 node49 1,4 -Beta -Mannan node82 node49->node82 node50->node49 Mannan node50->Mannan node51 node51->node14 node51->node30 node52 node52->node30 node53 node53->node30 node54 1.1.1.- node54->node41 node54->node42 node55 node55->node29 node55->node45 node56->node36 node57 Glyceraldehyde-3P node113 Glycolysis / Gluconeogenesis node57->node113 node58 node58->node11 node58->node56 node58->node57 node108 Glycerone-P node58->node108 node112 D-Glyceraldehyde node58->node112 node60 Mannosyl -3 -phosphoglycerate node59->node60 node61 node60->node61 Mannosylglycerate node61->Mannosylglycerate node63 GDP -4 -oxo-6 -deoxy-D -mannose node62->node63 node70 node63->node70 node73 node63->node73 node64 GDP -D -mannuronate node68 node64->node68 node65 delta-Dimer node66 node66->node65 node67 node67->node65 Alginate node68->Alginate node69->node64 node80 GDP -6 -deoxy-D -talose node70->node80 node71 node71->node63 node81 GDP -D -rhamnose node71->node81 node72 node72->node63 node72->node81 node79 GDP -L -Fucose node73->node79 node74 node78 L-Fucose -1P node74->node78 node74->node79 node75 node75->node78 node76 13 node77 L-Fucose node77->node75 node77->node76 L-Fucose node77->node114 node82->node30 node83 node83->node77 node84 L-Fuculose node83->node84 node85 node84->node85 node87 L-Fuculose -1P node85->node87 node86 node88 L-Lactaldehyde node86->node88 node87->node86 node89 4.1.2.- node89->node88 node90 2-Dehydro -3-deoxy -L-rhamnonate node89->node90 node91 node91->node90 node92 L-Rhamnonate node91->node92 node93 node93->node92 node94 L-Rhamnono -1,4-lactone node93->node94 node95 node95->node94 node96 L-Rhamnofuranose node95->node96 node97 L-Rhamnose node96->node97 node97->node96 node98 L-Rhamnulose node99 node98->node99 node101 L-Rhamnulose -1P node99->node101 node100 node100->node97 node100->node98 node102 node102->node101 node102->node108 node103 D-Lactaldehyde node104 node104->node103 node105 2-Dehydro -3-deoxy -D-fuconate node104->node105 node106 node106->node105 node107 D-Fuconate node106->node107 node109 node109->node11 node109->node56 node110 node110->node57 node110->node108 node111 node111->node57 node111->node112 Galactose metabolism->node4 node113->node31 node114->node64 Alginate->node66 Alginate->node67 Fructan Fructan->node15 Mannan->node52 Mannan->node53 print "