Ch. 14: Alt Pathways of Glucose Metabolism & Hexose Interconversions Flashcards
What is glucuronic acid? Essential part of what?
Glucose w/oxidized C6
GAGs
What reactions are glucuronic acid needed for?
Highly polar ➡️ detox rxns of insoluble compounds (bilirubin, steroids, drugs)
Enzymes used to synthesize glucuronic acid?
1) UDPG-dehydrogenase (UDP glucose ➡️ UDP glucuronic acid)
2) Glucuronyl-transferase (UDP glucuronic acid ➡️ glucuronides)
2 main products from conversion of D-glucuronic acid?
L-ascorbic acid (not in humans)
D-Xylulose 5-P (➡️ PPP)
Disorders of glucuronic acid metabolism:
L-gulonolactone oxidase deficiency?
Unable to convert L-gulonolactone ➡️ L-ascorbic acid
Requires Vitamin C in diet
Disorders of glucuronic acid metabolism:
NADP+ dependent xylitol dehydrogenase deficiency?
No conversion of L-xylulose ➡️ xylitol
Causes essential pentosuria (⬆️ L-xylulose in urine)
Why is metabolism of fructose important?
Unable to regulate fructose blood levels
Major pathway of dietary fructose metabolism?
D-fructose ➡️ fructose 1-P (fructokinase)
Fructose 1-P ➡️ D-glyceraldehyde (aldolase B)
Minor pathway of dietary fructose metabolism?
D-fructose ➡️ fructose 6-P (hexokinase)
Blocking which enzyme occurs in essential fructosuria? Hereditary fructose intolerance?
Fructokinase
Aldolase B
Which enzymes convert D-glucose ➡️ D-sorbitol ➡️ D-fructose? Cofactors for each rxn?
1) Aldose reductase, NADPH (when ⬆️ glucose)
2) Sorbitol dehydrogenase, NAD+
Characteristics of essential fructosuria?
Benign
⬆️ fructose in urine
Characteristics of hereditary fructose intolerance?
Traps fructose 1-P in cells
Hypoglycemia, jaundice, hepatomegaly, liver failure, hyperuricemia, lactic acidemia
Steps in metabolism of galactose? Enzymes at each step?
Galactose ➡️ galactose 1-P (galactokinase)
Galactose 1-P ➡️ glucose 1-P or UDP galactose (galactose 1-P uridyl transferase)
Disorders of galactose metabolism:
Galactosemia? Characteristics?
Galactose 1-P uridyl transferase deficiency
Galactosemia, galactosuria, liver damage, cataracts, intellectual disability
Disorders of galactose metabolism:
Galactokinase deficiency, characteristics?
Galactosemia, galactosuria
Galactose ➡️ ⬆️ galactitol (aldose reductase
Can cause cataracts
How is lactose synthesized?
UDP-galactose + glucose ➡️ lactose (lactose synthase)
Which 2 proteins make up lactose synthase?
Beta-D-galactosyltransferase (protein A)
alpha-lactalbumin (protein B)
Metabolism of amino sugars:
How is fructose 6-P ➡️ glucosamine 6-P?
Aminotransferase, with gln ➡️ glu
Metabolism of amino sugars:
End products of metabolism of glucosamine 6-P?
GAGs (chondroitins, heparin)
glycoproteins
Sialic acid
Gangliosides
Where does pentose phosphate pathway occur?
Cytosol
3 function of PPP?
1) supply NADPH
2) supply ribulose 5-P
3) generate glycolysis intermediates
PPP:
Steps from glucose 6-P ➡️ ribulose 5-P? Enzymes for each step?
1) Glucose 6-P ➡️ 6-phosphogluconate (G6P dehydrogenase)
2) 6-phosphogluconate ➡️ ribulose 5-P (6-phosphogluconate dehydrogenase)
1 NADPH generated at each step
2 diff pathways for ribulose 5-P?
1) ➡️ ribose 5-P (ribose 5-P isomerase) ➡️ nucleic acid biosynthesis
2) ➡️ xylulose 5-P ➡️ glycolysis intermediates