The oxoacyl-coenzyme A thiolases of animal tissues

Abstract

1. The activities and relative 3-oxoacyl-CoA substrate specificities of oxoacyl-CoA thiolase were determined in a large number of animal tissues. The relative activities with different 3-oxoacyl-CoA substrates varied widely in different tissues and, in addition, the activity as measured with acetoacetyl-CoA (but not with other longer-carbon-chain acyl-CoA substrates) was activated by K(+). 2. These properties were due to the presence, in different proportions in each tissue, of three classes of thiolase, all of which use acetoacetyl-CoA as substrate but which have different intracellular locations and substrate specificities and which differ also in kinetic and chromatographic behaviour. 3. Cytoplasmic thiolase activity was found to be widely distributed among different tissues and was due to an acetoacetyl-CoA-specific thiolase. This cytoplasmic activity was found to account for a significant proportion of the total tissue activity towards acetoacetyl-CoA in several tissues, and especially in the brain of newborn rats. 4. Mitochondrial thiolase activity towards acetoacetyl-CoA was due to two different classes of enzyme whose relative amounts varied with the tissue type. An oxoacyl-CoA thiolase of general specificity for the acyl-CoA substrate constituted one class, the other being a specific acetoacetyl-CoA thiolase that differed from its cytoplasmic counterpart in being greatly stimulated by K(+). 5. This activation by K(+) made it possible to calculate the tissue contents of mitochondrial acetoacetyl-CoA thiolase and mitochondrial oxoacyl-CoA thiolase from measurements of activity with acetoacetyl-CoA in tissue extracts under defined conditions. 6. The properties and the different thiolases and their tissue distribution is discussed with respect to their possible roles in metabolism.

The Presence of a New 3‐Oxoacyl‐CoA Thiolase in Rat Liver Peroxisomes

“…Rat liver thiolases have been separated by DEAEcellulose and phosphocellulose column chromatography [1,20]. By this separation procedure with use of acetoacetyl-CoA and 3-oxooctanoyl-CoA as the substrates, it was revealed that a novel thiolase was markedly increased in the livers of rats when fed with the di(2-ethylhexy1)phthalate-containing diet.…”

A simple purification of acetoacetate—succinate CoA‐transferase using substrate elution chromatography

“…The buffer anion used was sulphate rather than chloride as monovalent anions inhibit the enzyme [2]. The extinction coefficient of acetoacetyl-CoA under these conditions is 16.9 X103 litre.mo1-1 [9].…”

Identification, purification and characterization of an acetoacetyl-CoA thiolase from rat liver peroxisomes

“…Asterisks indicate the occurrence of substrate inhibition. reported before by others for cTh [1,3]. These similarities in chromatographic behaviour as well as the low activity of pTh in whole peroxisomes in comparison to the activities of the known peroxisomal thiolases suggested that we might have purified a contaminant cytosolic acetoacetyl-CoA thiolase from the peroxisomal fraction.…”

“…Acetoacetyl-CoA thiolases catalyse the following reversible reaction: acetoacetyl ÿ CoA 1 CoA Y 2 acetyl ÿ CoA and do not react with medium and long chain 3-oxoacyl-CoAs. In the liver the enzymes mediate mainly acetoacetyl-CoA formation, whereas in extrahepatic tissues the mitochondrial reaction proceeds in the direction of acetyl-CoA synthesis [1,7,8].…”

“…The subunit of mTh is synthesized as a 45 kDa precursor with an Nterminal targeting presequence and converted to the mature form by proteolytic processing upon import into the mitochondria [6]. Enzymatically, the mTh can be distinguished from the cTh and other 3-oxoacyl-CoA thiolases (see below) by its requirement for K 1 ions for activation [1]. Acetoacetyl-CoA thiolases catalyse the following reversible reaction: acetoacetyl ÿ CoA 1 CoA Y 2 acetyl ÿ CoA and do not react with medium and long chain 3-oxoacyl-CoAs.…”