On the regulation of cold-labile cytosolic and of mitochondrial acetyl-CoA hydrolase in rat liver

To examine whether cytosolic acetyl-CoA hydrolase in rat liver is involved in regulation of cholesterol biosynthesis, we investigated the alteration of the enzyme activity under conditions of stimulation (cholestyramine treatment) and suppression [cholesterol feeding, a potent competitive inhibitor of microsomal 3-hydroxy-3-methylglutaryl-CoA reductase (CS 514) treatment, and a hypolipidemic drug [alpha-(p-chlorophenoxy)isobutyric acid, CPIB] injection) of cholesterol biosynthesis. The enzyme activity in rat liver increased significantly in the early diabetic, cholesterol-fed, CS 514-, and CPIB-treated groups, but no change in its activity was observed in chronic diabetic groups. Cholestyramine treatment to cholesterol-fed rats made the enzyme activity return to the initial level. When chronic diabetic rats were given a cholesterol diet or treated with CS 514 or CPIB, the activity increased significantly. Inhibition of cholesterol biosynthesis caused by these treatments induced increase in the enzyme activity with increase in the enzyme protein, judging from results obtained by enzyme-linked immunosorbent assay. These results suggest that this enzyme has a physiological role in maintenance of the equilibrium between the cytosolic acetyl-CoA concentration and CoA-SH pool for cholesterol metabolism.

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Binding of nucleotides to an extramitochondrial acetyl-CoA hydrolase from rat liver

Biochemistry ◽

10.1021/bi00413a036 ◽

1988 ◽

Vol 27 (13) ◽

pp. 4822-4826 ◽

Cited By ~ 5

Author(s):

Yoko Nakanishi ◽

Fumihide Isohashi ◽

Shoji Ebisuno ◽

Yukiya Sakamoto

Keyword(s):

Rat Liver ◽

Acetyl Coa ◽

Coa Hydrolase

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Acetyl-coenzyme A hydrolase, an artifact? The conversion of acetyl-coenzyme A into acetate by the combined action of carnitine acetyltransferase and acetylcarnitine hydrolase

Biochemical Journal ◽

10.1042/bj1520167 ◽

1975 ◽

Vol 152 (2) ◽

pp. 167-172 ◽

Cited By ~ 13

Author(s):

N. D. Costa ◽

A. M. Snoswell

Keyword(s):

Rat Liver ◽

Mitochondrial Membrane ◽

Hydrolase Activity ◽

Carnitine Acetyltransferase ◽

Inner Mitochondrial Membrane ◽

Acetyl Coa ◽

Acetyl Coenzyme A ◽

Sheep Liver ◽

Liver Homogenates ◽

Coa Hydrolase

1. The nature of the acetyl-CoA hydrolase (EC 3.1.2.1) reaction in rat and sheep liver homogenates was investigated. 2. The activity determined in an incubated system was 5.10 and 3.28nmol/min per mg of protein for rat and sheep liver homogenate respectively. This activity was not affected by the addition of l-carnitine, but was decreased by the addition of d-carnitine. 3. No acetyl-CoA hydrolase activity could be detected in rat or sheep liver homogenates first treated with Sephadex G-25. This treatment decreased the carnitine concentrations of the homogenates to about one-twentieth. Subsequent addition of l-carnitine, but not d-carnitine, restored the apparent acetyl-CoA hydrolase activity. 4. Sephadex treatment did not affect acetyl-carnitine hydrolase activity of the homogenates, which was 5.8 and 8.1nmol/min per mg of protein respectively for rat and sheep liver. 5. Direct spectrophotometric assay of acetyl-CoA hydrolase, based on the reaction of CoA released with 5,5′-dithiobis-(2-nitrobenzoic acid), clearly demonstrated that after Sephadex treatment no activity could be measured. 6. Carnitine acetyltransferase (EC 2.3.1.7) activity measured in the same assay system in response to added l-carnitine was very low in normal rat liver homogenates, owing to the apparent high acetyl-CoA hydrolase activity, but was increased markedly after Sephadex treatment. The Vmax. for this enzyme in rat liver homogenates was increased from 3.4 to 14.8nmol/min per mg of protein whereas the Km for l-carnitine was decreased from 936 to 32μm after Sephadex treatment. 7. Acetyl-CoA hydrolase activity could be demonstrated in disrupted rat liver mitochondria but not in separated outer or inner mitochondrial membrane fractions. Activity could be demonstrated after recombination of outer and inner mitochondrial membrane fractions. The outer mitochondrial membrane fraction showed acetylcarnitine hydrolase activity and the inner mitochondrial membrane fraction showed carnitine acetyltransferase activity. 8. The results presented here demonstrate that acetyl-CoA hydrolase activity in rat and sheep liver is an artifact and the activity is due to the combined activity of carnitine acetyltransferase and acetylcarnitine hydrolase.

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