Purification and partial characterization of 3-hydroxyisobutyryl-coenzyme A hydrolase of rat liver.
An unusual feature of valine catabolism is a reaction in which an intermediate of its catabolic pathway, (S)-3-hydroxyisobutyryl-CoA, is hydrolyzed to give the free acid and CoA-SH. The enzyme responsible for this reaction, 3-hydroxyisobutyryl-CoA hydrolase (EC 3.1.2.4), was purified 7200-fold from rat liver in this study. The purified enzyme consists of a single polypeptide with an M(r) of 36,000 in the native and denatured forms. The hydrolase is highly specific for (S)-3-hydroxyisobutyryl-CoA and 3-hydroxypropionyl-CoA (Km, 6 and 25 microM, respectively) with optimal activity around pH 8. The turnover rate of the enzyme for (S)-3-hydroxyisobutyryl-CoA is 270 s-1, which is high relative to other enzymes of the valine pathway. Likewise, activity of the enzyme expressed on a wet weight basis is also very high in the major tissues of the rat. These findings suggest that rapid destruction of (S)-3-hydroxyisobutyryl-CoA produced during valine catabolism is physiologically important. We propose that the need for a mechanism to protect cells against the toxic effects of methacrylyl-CoA, which is maintained in equilibrium with (S)-3-hydroxyisobutyryl-CoA by crotonase, explains why valine catabolism involves this enzyme and why its tissue activity is so high.
Shimomura
Y
Y
Department of Bioscience, Nagoya Institute of Technology, Japan.
Murakami
T
T
Fujitsuka
N
N
Nakai
N
N
Sato
Y
Y
Sugiyama
S
S
Shimomura
N
N
Irwin
J
J
Hawes
J W
JW
Harris
R A
RA
D000214:Acyl Coenzyme A / Q000378:metabolism; D000818:Animals; D002412:Cations; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009711:Nucleotides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity; D013869:Thiolester Hydrolases / Q000302:isolation & purification* / Q000378:metabolism; D014018:Tissue Distribution
D000214:Acyl Coenzyme A; D002412:Cations; D009711:Nucleotides; C015357:methylmalonyl-coenzyme A; D013869:Thiolester Hydrolases; C035908:3-hydroxyisobutyryl-CoA hydrolase