Substrate specificities of 3-oxoacyl-CoA thiolase A and sterol carrier protein 2/3-oxoacyl-CoA thiolase purified from normal rat liver peroxisomes. Sterol carrier protein 2/3-oxoacyl-CoA thiolase is involved in the metabolism of 2-methyl-branched fatty acids and bile acid intermediates

J Biol Chem. 1997 Oct 10;272(41):26023-31. doi: 10.1074/jbc.272.41.26023.


The two main thiolase activities present in isolated peroxisomes from normal rat liver were purified to near homogeneity. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the first enzyme preparation displayed a single band of 41 kDa that was identified as 3-oxoacyl-CoA thiolase A (thiolase A) by N-terminal amino acid sequencing. The second enzyme preparation consisted of a 58- and a 46-kDa band. The 58-kDa polypeptide reacted with antibodies raised against either sterol carrier protein 2 or the thiolase domain of sterol carrier protein 2/3-oxoacyl-CoA thiolase (SCP-2/thiolase), formerly also called sterol carrier protein X, whereas the 46-kDa polypeptide reacted only with the antibodies raised against the thiolase domain. Internal peptide sequencing confirmed that the 58-kDa polypeptide is SCP-2/thiolase and that the 46-kDa polypeptide is the thiolase domain of SCP-2/thiolase. Thiolase A catalyzed the cleavage of short, medium, and long straight chain 3-oxoacyl-CoAs, medium chain 3-oxoacyl-CoAs being the best substrates. The enzyme was inactive with the 2-methyl-branched 3-oxo-2-methylpalmitoyl-CoA and with the bile acid intermediate 24-oxo-trihydroxycoprostanoyl-CoA. SCP-2/thiolase was active with medium and long straight chain 3-oxoacyl-CoAs but also with the 2-methyl-branched 3-oxoacyl-CoA and the bile acid intermediate. In peroxisomal extracts, more than 90% of the thiolase activity toward straight chain 3-oxoacyl-CoAs was associated with thiolase A. Kinetic parameters (Km and Vmax) were determined for each enzyme with the different substrates. Our results indicate the following: 1) the two (main) thiolases present in peroxisomes from normal rat liver are thiolase A and SCP-2/thiolase; 2) thiolase A is responsible for the thiolytic cleavage of straight chain 3-oxoacyl-CoAs; and 3) SCP-2/thiolase is responsible for the thiolytic cleavage of the 3-oxoacyl-CoA derivatives of 2-methyl-branched fatty acids and the side chain of cholesterol.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetyl-CoA C-Acetyltransferase / isolation & purification
  • Acetyl-CoA C-Acetyltransferase / metabolism*
  • Animals
  • Bile Acids and Salts / metabolism*
  • Carrier Proteins / isolation & purification
  • Carrier Proteins / metabolism*
  • Chromatography, High Pressure Liquid
  • Fatty Acids / metabolism*
  • Hydrogen-Ion Concentration
  • Kinetics
  • Liver / chemistry
  • Liver / enzymology*
  • Male
  • Methylation
  • Microbodies / chemistry
  • Microbodies / enzymology*
  • Rats
  • Rats, Wistar
  • Spectrophotometry, Atomic
  • Sterols / isolation & purification
  • Sterols / metabolism*
  • Substrate Specificity


  • Bile Acids and Salts
  • Carrier Proteins
  • Fatty Acids
  • Sterols
  • sterol carrier proteins
  • Acetyl-CoA C-Acetyltransferase