Summary notes - The uronic acid pathway PDF

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Summary notes - The uronic acid pathway Pathway The Uronic acids are a class of sugar acids with both carbonyl and carboxylic acid functional groups. They are sugars in which the terminal carbon’s hydroxyl group has been oxidized to a carboxylic acid. The Oxidation of the terminal aldehyde instead yields an aldonic acid, while oxidation of both the terminal hydroxyl group and the aldehyde yields an aldaric acid. The names of uronic acids are generally based on their parent sugars, for example, the uronic acid analog of glucose is glucuronic acid. Uronic acids derived from hexoses are known as hexuronic acids and uronic acids derived from pentoses are known as penturonic acids. The URONIC ACID PATHWAY The glucuronic acid pathway is a quantitatively minor route of glucose metabolism. Like the pentose phosphate pathway, it provides biosynthetic precursors and inter-converts some less common sugars to ones that can be metabolized. The URONIC ACID PATHWAY Uronic acid pathway is an alternative oxidative pathway for glucose metabolism. It catalyzes the conversion of glucose to glucuronic acid, ascorbic acid, and pentoses. It does not lead to the formation of ATP.

The Location In cytoplasm of the cell Tissue distribution: Liver and Adipose tissue freestar Steps of Uronic Acid Pathway Steps of Uronic Acid Pathway STEP 1: Glucose 6-phosphate is converted to Glucose1-phosphate via phosphoglucomutase. STEP 2: Glucose 1-phosphate reacts with uridinetriphosphate (UTP) via UDP glucosepyrophosphorylase to form UDP

L- Gulonate The L-gulonate It is the direct precursor of ascorbate in those animals capable of synthesizing this vitamin, in an NADPH-dependent reaction. In humans, ascorbic acid cannot be synthesized because of the absence of L-gulonolactone oxidase. The STEP 6: Oxidation of L-Udonic acid L-gulonic acid may be oxidized to 3-keto-Lgulonicacid via β -L-hydroxy acid dehydrogenase.

The NADH is generated. STEP 7: Decarboxylation of 3-Keto-L-Gulonic Acid They are Followed by decarboxylation of 3keto-L-gulonicacid to form L-xylulose,a ketopentose via β-L- gulonate decarboxylase ; here, carbon 1 of 3-keto-L-gulonic acid is released as CO2. STEP 8: Oxidation of L-Xylulose L-xylulose is then reduced to xylitol via xylitoldehydrogenase (or xylulosereductase) STEP 9: Reoxidation of Xylitol STEP 10: Phosphorylation of D-Xylulose D-xylulose is phosphorylated at carbon 5 to form D-xylulose 5-phosphat via xylulose kinase Further metabolized via the HMP Shunt Converted to intermediates of glycolysis for energy production

The Regulation of Uronic Pathway Administration of drugs i.e. Chlorobutanol & Barbital significantly increases the uronic acid pathway. Certain drugs are also found to enhance the synthesis of Ascorbic acid. The Significance of Uronic Pathway It is an alternative oxidative pathway for glucose. It is concerned with the synthesis of glucuronic acid, pentoses & vitamin-ascorbic acid (except

glucose. STEP 3: UDP glucose is oxidized at C6 by a 2step process via an NAD +-dependent UDP glucosedehydrogenase to form UDP glucuronic acid. STEP 4: UDP glucuronic acid is hydrolysed to form UDP and D-glucuronic acid. UDP-glucuronate The Source of glucuronate for reactions involving its incorporation into proteoglycans. conjugated to nonpolar acceptor molecules such as steroid hormones, some drugs, bilirubin, or other foreign compounds in the liver for easier excretion via the bile. STEP 5: Oxidation of D-glucuronic acid to Lgulonic acid via L- gulonic dehydrogenase in the presence of NADPH2.

in primates & guinea pigs). The Major function is to produce D-Glucuronic acid which is required for: Detoxification of foreign chemicals and synthesis of mucopolysaccharides. Many wastes in the human body are excreted in the urine as their glucuronate salts, Iduronic acid is a component of some structural complexes such as proteoglycans....