The valine catabolic pathway in human liver: Effect of cirrhosis on enzyme activities

• Published in: Hepatology (Baltimore, Md.) Vol. 24; no. 6; pp. 1395 - 1398
• Main Authors: Taniguchi, K, Nonami, T, Nakao, A, Harada, A, Kurokawa, T, Sugiyama, S, Fujitsuka, N, Shimomura, Y, Hutson, S M, Harris, R A, Takagi, H
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.12.1996; Wiley
• Subjects: 3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); Animals; Biological and medical sciences; Carcinoma, Hepatocellular - enzymology; Enoyl-CoA Hydratase - metabolism; Female; Gastroenterology. Liver. Pancreas. Abdomen; Humans; Ketone Oxidoreductases - metabolism; Liver - enzymology; Liver Cirrhosis - enzymology; Liver Neoplasms - enzymology; Liver. Biliary tract. Portal circulation. Exocrine pancreas; Male; Medical sciences; Middle Aged; Multienzyme Complexes - metabolism; Other diseases. Semiology; Rats; Reference Values; Species Specificity; Thiolester Hydrolases - metabolism; Transaminases - metabolism; Valine - metabolism; 3-Hydroxyisobutyryl-CoA hydrolase; Branched-chain-amino-acid transaminase; Liver; Hepatic disease; Esterases; Lyases; Metabolic pathway; Result; Enoyl-CoA hydratase; Enzymatic activity; Biological effect; Human; Enzyme; Transferases; Thiolester hydrolases; Cirrhosis; Valine; Transaminases; Digestive diseases; Hydrolases; Catabolism; Oxidoreductases; Carbon-oxygen lyases; Hydro-lyases; 3-Methyl-2-oxobutanoate dehydrogenase (lipoamide)
• ISSN: 0270-9139; 1527-3350
• DOI: 10.1002/hep.510240614

The activities of key enzymes in the valine catabolic pathway–branched‐chain aminotransferase, branched‐chain alpha‐keto acid dehydrogenase complex, methacrylyl (MC)‐coenzyme A (CoA) hydratase (crotonase), and 3‐ hydroxyisobutyryl‐CoA (HIB‐CoA) hydrolase–were measured in normal and cirrhotic human livers. Unlike rat liver, which does not contain branched‐chain aminotransferase, the aminotransferase activity in the normal liver was measurable and is increased somewhat in cirrhosis of the human liver. The total activity of branched‐chain alpha‐keto acid dehydrogenase complex in the normal human liver was approximately 1% of that in rat liver, and 20% to 30% of the complex was in the active form in both normal and cirrhotic livers. Only the actual activity of the enzyme was significantly decreased by cirrhosis. These results suggest that human liver is less active than rat liver in the catabolism of branched‐chain amino and alpha‐keto acids. Activities of MC‐CoA hydratase and HIB‐CoA hydrolase in human liver were very high compared with that of branched‐chain alpha‐keto acid dehydrogenase complex, suggesting an important role for these enzymes in catabolism of a potentially toxic compound, MC‐CoA, formed as an intermediate in the catabolism of valine and isobutyrate. Cirrhosis resulted in a significant decrease in HIB‐CoA hydrolase activity but had no effect on the citrate synthase activity, suggesting that the decrease in HIB‐CoA hydrolase activity does not reflect a general decrease in mitochondria but that it may contribute to cellular damage that culminates in liver failure.