Studies on the hydrolysis and utilization of long chain acyl CoA thioesters by liver microsomes

The activities of long-chain acyl-CoA hydrolase (palmitoyl-CoA hydrolase, EC 3.1.2.2) and long-chain acyl-L-carnitine hydrolase, EC 3.1.1.28) in brown adipose tissue from cold-exposed and control guinea pigs were studied. Mitochondria from cold-exposed animals hydrolysed 21 nmol of palmitoyl-CoA/min per mg of protein and 1.3 nmol of palmitoyl-L-carnitine/min per mg of protein, and the specific activities were respectively 2 and 5 times as high in cold-exposed as in control animals. The subcellular-localization studies showed that both the long-chain acyl-CoA hydrolase and long-chain acyl-L-carnitine hydrolase were localized in the mitochondria. A location also in the soluble fraction cannot be excluded. The long-chain acyl-CoA hydrolase activity was doubled when the mitochondria were disrupted; this indicates that the enzyme is localized in the matrix compartment.

Section: Discussionmentioning

confidence: 99%

Intracellular localization of long-chain acyl-coenzyme A hydrolase and acyl-L-carnitine hydrolase in brown adipose tissue from guinea pigs

Berge¹,

Slinde²,

Farstad³

1979

“…In contrast with phosphohydrolase, no definite metabolic significance has been assigned to palmitoyl-CoA hydrolase (McMurray & Magee, 1972), although its properties have been described in some detail (Barden & Cleland, 1969;Jezyk & Hughes, 1971; Barber & Lands, 1971;Jansen & Hulsmann, 1973 A number of controversial results for the acylCoA-glycerol 3-phosphate and acyl-CoA-monoacylglycerol 3-phosphate acyltransferase reactions have previously been reported, partly because of unsuitable assay methods. In our assay with…”

Section: Discussionmentioning

confidence: 99%

Phosphatidate phosphohydrolase and palmitoyl-coenzyme A hydrolase in cardiac subcellular fractions of hyperthyroid rabbits and cardiomyopathic hamsters

Kako

Patterson

1975

Activities of phosphatidate phosphohydrolase and palmitoyl-CoA hydrolase were determined in cardiac subcellular fractions prepared from rabbits which had received tri-iodothyronine and from hamsters with hereditary cardiomyopathy (strain BIO 14.6). 1. Both mitochondrial and microsomal fractions of hyperthyroid rabbit hearts produced 4-5 times as much diacylglycerol 3-phosphate from glycerol 3-phosphate and palmitate as did those of euthyroid hearts. 2. Phosphatidate phosphohydrolase, measured with phosphatidate emulsion, was activated by 1 mM-Mg2+ in all but the mitochondrial fraction of euthyroid rabbit hearts. The activation was more pronounced in subcellular fractions isolated from hyperthyroid hearts, so that the measured activities were significantly increased above those of the controls. The highest activity was found in the microsomal and lysosomal fractions. 3. In the absence of Mg2+ during incubation, the difference in phosphohydrolase activities between eu-and hyper-thyroid states was not significant. 4. The phosphohydrolase of subcellular fractions of control hamsters did not respond to addition of 0.5-8.0mM-Mg2+. The enzyme from cardiomyopathic hearts was slightly inhibited by this bivalent cation and therefore significant increases in activity were observed only in the absence of Mg2+ from the assay system. 5. The rate of reaction by soluble phosphatidate phosphohydrolase was similar regardless of the nature of the substrate. Both when microsomal-bound phosphatidate was used as the substrate and when phosphatidate suspension was used, the activity of soluble enzyme was lower than that of the microsomal and lysosomal enzymes measured with phosphatidate suspension; this was especially so when the assay was carried out in the absence of Mg2+. Neither tri-iodothyronine nor cardiomyopathy influenced the soluble phosphohydrolase activity in the two species. 6. Neither tri-iodothyronine nor cardiomyopathy significantly changed palmitoyl-CoA hydrolase activities in subcellular fractions. 7. Microsomal diacylglycerol acyltransferase and myocardial triacylglycerol content were also unchanged in the hyperthyroid state.

“…Long-chain fatty acyl-CoA thioesterase (palmitoyl-CoA hydrolase, EC 3.1.2.2) is present in various mammalian tissues and seems to be involved in both lipid and carbohydrate metabolism (Kurooka et al, 1972;Porter & Long, 1956). However, no definite metabolic significance has been assigned to palmitoyl-CoA hydrolase (McMurray & Magee, 1972), although its properties have been described in some detail (Barden & Cleland, 1969;Jezyk & Hughes, 1971; Barber & Lands, 1971;.…”

mentioning

confidence: 99%

Differences between microsomal and mitochondrial-matrix palmitoyl-coenzyme A hydrolase, and palmitoyl-l-carnitine hydrolase from rat liver

Berge¹,

Døssland²

1979

Palmitoyl-CoA hydrolase (EC 3.1.2.2) and palmitoyl-L-carnitine hydrolase (EC 3.1.1.28) activities from rat liver were investigated. 1. Microsomal and mitochondrial-matrix palmitoyl-CoA hydrolase activities had similar pH and temperature optima, although the activities showed different temperature stability. They were inhibited by Pb2+ and Zn2+. The palmitoyl-CoA hydrolase activities in microsomal fraction and mitochondrial matrix were differently affected by the addition of Mg2+, Ca2+, Co2+, K+ and Na+ to the reaction mixture. ATP, ADP and NAD+ stimulated the microsomal activity and inhibited the mitochondrial-matrix enzyme. The activity of both the microsomal and mitochondrial-matrix hydrolase enzymes was specific for long-chain fatty acyl-CoA esters (C12-C18), with the highest activity for palmitoyl-CoA. The apparent Km for palmitoyl-CoA was 47 microM for the microsomal enzyme and 17 microM for the mitochondrial-matrix enzyme. 2. The palmitoyl-CoA hydrolase and palmitoyl-L-carnitine hydrolase activities of microsomal fraction had similar pH optima and were stimulated by dithiothreitol, but were affected differently by the addition of Pb2+, Mg2+, Ca2+, Mn2+ and cysteine. The two enzymes had different temperature-sensitivities. 3. The data strongly suggest that palmitoyl-CoA hydrolase and palmitoyl-L-carnitine hydrolase are separate microsomal enzymes, and that the hydrolysis of palmitoyl-CoA in the microsomal fraction and mitochondria matrix was catalysed by two different enzymes.