Glucuronate degradation and

Most hormones have a half-life in the blood of only a few minutes because they are cleared or metabolized very rapidly. The rapid degradation of hormones allows target cells to respond transiently. Polypeptide hormones are removed from the circulation by serum and cell surface proteases, by endocytosis followed by lysosomal degradation, and by glomerular filtration in the kidney. Steroid hormones are taken up by the liver and metabolized to inactive forms, which are excreted into the bile duct or back into the blood for removal by the kidneys. Catecholamines are metaboli-cally inactivated by O-methylation, by deamination, and by conjugation with sulfate or glucuronic acid. 

Studies on the fate of D-glucuronic acid labeled with C14 have been mentioned previously in this review (Section IV, 2b). It is evident from these reports that extensive degradation of the molecule takes place, revealed by the large amount of carbon dioxide recovered. It is also clear that fragments of the acid are available for the resynthesis of D-glucuronic acid, and hence, perhaps, of D-glucose as well. 

Understand the mechanisms for /V-acetylglucosamine biosynthesis and degradation of fructose and galactose, and inborn errors of metabolism associated with these pathways Appreciate the physiologic role of the glucuronate pathway and the inborn errors of metabolism associated with its malfunction ... 

Glucuronic acid and sialic acid are normally present in conjugated forms. After degradation of these components in lysosomes, the free monosaccharides are released by a specific membrane transport system. The lysosomal sialic acid transporter from rat liver has been purified to apparent homogeneity in a reconstitutively active form. The transporter recognized structurally different types of acidic monosaccharides such as sialic acid, glucuronic acid, and iduronic acid. The transport was proton gradient dependent, and saturable with a of approximately 0.4mM [211]. 

When heme proteins are degraded in mammals, the polypeptides are hydrolyzed to amino acids while the heme groups are freed of their iron, which is salvaged, and are converted to bilirubin. After transport to the liver, bilirubin is coupled to glucuronic acid and the conjugated bilirubin is excreted into bile as the principal bile pigment. When increased production or decreased excretion of bilirubin causes its plasma concentration to exceed 0.1-1.0 mg/dL (2-17 /rmol/L), it diifuses into tissues and... 

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