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Several nucleotides can activate sugars. In the case of glucose for glycogen synthesis it is UTP. See next page. The first reaction a), is reversible but it is coupled to b) that releases -5 kcal/mol and favors reaction a).
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Several nucleotides can activate sugars. In the case of glucose for glycogen synthesis it is UTP. See next page
The first reaction a), is reversible but it is coupled to b) that releases -5 kcal/mol and favors reaction a).
Sugar nucleotides of glucose or of any other carbohydrate are called activated because sugars bound to nucleotides can be transferred by specific enzymes to proteins and other molecules or can be subjected to enzymatic modifications possible only with activated sugars.
UDP-glucuronic is important for detoxification of many drugs and metabolites. Below is shown the formula of conjugated bilirubin:
We, primates, lost the ability to make ascorbate. Therefore we are genetically deficient.
Fructose is an ketose, therefore it
is not a substrate of aldose
reductase and causes no cataracts.
Glucose and galactose are aldoses
and they do cause cataracts
Synthesis of uridinediphosphoglucose or UDPGlu
Do you remember phosphoglyceromutase? Any similarities with phosphoglucomutase?
PPi is hydrolyzed by a pyrophosphorylase in a reaction coupled with the pyrophosphorylase
to dissipate energy as heat thus making the synthesis of UDP-Glu thermodynamically favorable.
Deficiency of branching enzyme gives long branches. Causes death at about to years of age. Andersen’s disease
The content of glycogen is about 10 % of the wet weight of the liver and 2% of muscle.
Glycogen synthase only adds glucoses to an existing chain of at least 4 glucose residues. Glycogenin acts by catalyzing the addition of glucose to itself (autocatalysis) by first binding glucose from UDP-glucose to the hydroxyl of Tyr-194 from UDP-glucose, by glycogenin's glucosyltransferase. Once sufficient residues have been added, glycogen synthase takes over extending the chain. Glycogenin remains covalently attached to the reducing end of glycogen.
The breakdown of glycogen and entry into glycolysis as glucose-6-P is achieved by three enzymes: glycogen phosphorylase, debranching enzyme and phosphoglucomutase.
Glycogen phosphorylase produces glucose-1-P plus limit dextrin.
The debranching enzyme has a transferase and glycosidase (hydrolase) activities.
Hexokinase is bypassed when glucose comes from glycogen!
Deficiency of phosphorylase (Mc Adler’s) causes muscle cramps and no lactate formation during exercise.
Deficiency of debranching enzyme causes accumulation of limit dextrin
In the next lecture we will begin with regulatory mechanisms involved in