The availability of carnitine acetyltransferase in mitochondria from guinea-pig liver and other tissues

Barker, Paul D.; Fincham, N.J.; Hardwick, D C

doi:10.1042/bj1100739

Cited by 31 publications

(17 citation statements)

References 26 publications

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“…A certain discrepancy appears to exist with the findings of Barker et al [7]. These authors measured activities of carnitine acetyltransferase in intact and lysed mitochondria (Liver and mammary gland) and found little or no enzyme activity available to external acetyl-CoA in intact mitochondria.…”

Section: Fig 3 Proposed Scheme Of Localization and Function Of Extecontrasting

confidence: 48%

“…It has been shown, however, that glutamate dehydrogenase is located within the inner mitochondrial compartment [lo, 14,171 and may therefore only be related to the activity of carnitine acetyltransferase within this compartment. Our results indicate that carnitine acetyltransferase of the external mitochondrial compartment is easily extractable and may be set free even by gentle mechanical treatment.Intactness of the external mitochondrial compartment may be judged from the activity level of adenylate kinase, and this enzyme was not included into the studies of Barker et al [7]. Another possible explanation is, that in lipogenetic tissues mitochondrial carnitine acetyltransferase functions mainly with respect to carnitine-dependent transport of acetyl-CoA into the extramitochondrial compartment.…”

Section: Fig 3 Proposed Scheme Of Localization and Function Of Extementioning

confidence: 99%

“…Findings of Beenakkers et al [5,6] and Barker et al [7] suggest the whole cellular activity of carnitine acetyltransferase is located exclusively within the mitochondria. Barker et al concluded that little or no carnitine acetyltransferase is available, in vivo, to acetyl-CoA outside the mitochondria of liver or mammary gland of goat, guinea pig, and rat [7]. On the other hand, Beenakkers and Henderson [6] showed that flight muscle mitochondria of the locust contain two forms of carnitine acetyltransferase, one easily extractable, the other one more tightly attached to the mitochondrial membranes.…”

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confidence: 99%

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Localization and Function of External and Internal Carnitine Acetyltransferases in Mitochondria of Rat Liver and Pig Kidney

Brdiczka

Gerbitz

Pette

1969

European Journal of Biochemistry

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Subfractionation of rat liver mitochondria by the "digitonin method" revealed that carnitine acetyltransferase is present in two different compartments. The major part of the mitochondrial activity of this enzyme is found to be located in the inner mitochondrial compartment which contains also the soluble enzymes of the citric acid cycle, fatty acid oxidation and amino metabolism. At least 25 O/ , , of the total mitochondrial activity of carnitine acetyltransferase can be assigned to the outer mitochondrial compartment. The localization of this "external" carnitine acetyltransferase corresponds thus to that of mitochondrial adenylate kinase. Carnitine dependent oxidation of acetyl-CoA was studied in pig kidney mitochondria after treatment with low digitonin concentrations. It was found that oxidation of acetyl-CoA in the presence of carnitine depends on the amount of carnitine acetyltransferase present in the outer mitochondrial compartment.Extraction of external carnitine acetyltransferase decreases the oxidation rate of acetyl-CoA + carnitine. This may be partly restored by re-addition of extracted external carnitine acetyltransferase. Relatively high digitonin concentrations (0.75 mg/lO mg mitochondrial protein) render inner mitochondrial membrane permeable to acetyl-CoA. It is concluded that the inner membrane is a barrier to acetyl-CoA and that transport of acetyl-CoA across this membrane is mediated by the function of external and internal carnitine acetyltransferase.As shown by Fritz and Yue [i], acetyl CoA is unable to penetrate mitochondrial membranes. On the other hand, transport of acetyl CoA both into and out of mitochondria occurs in thc presence of carnitine [I -31. Because of these findings, carnitine acetyltransferase which catalyses the reversible acetylation of carnitine by acetyl-CoA, is believed to mediate transport of acetyl groups across the mitochondrial membranes. This mechanism of acetyl transfer should be linked to the presence of carnitine acetyltransferases both outside and inside the mitochondrial membrane which is impermeable to acetyl-

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Section: Fig 3 Proposed Scheme Of Localization and Function Of Extecontrasting

confidence: 48%

Section: Fig 3 Proposed Scheme Of Localization and Function Of Extementioning

confidence: 99%

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confidence: 99%

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Localization and Function of External and Internal Carnitine Acetyltransferases in Mitochondria of Rat Liver and Pig Kidney

Brdiczka

Gerbitz

Pette

1969

European Journal of Biochemistry

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“…CAT by the method of Barker et al [2], CPT by a modification of the method of Bieber [4,8]: 0.96 mg/ml palmitoyl-CoA, 0.1 ml; 1 m Tris (0.1 ml) 50 itim EDTA, 0.025 ml; 20 mg/ml (//-carnitine 0.1 ml; and 4 mg/ml DTNB (pH 7.5) 0.025 ml in a final volume of 1 ml. The blank always contained all the ingredients except carnitine.…”

Section: Methodsmentioning

confidence: 99%

The Role of Carnitine in Subcutaneous White Adipose Tissue from Newborn Infants

Novák¹,

Hahn²,

Penn³

et al. 1973

Neonatology

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Carnitineacetyltransferase (CAT) and carnitinepalmitoyltransferase (CPT) and the carnitine content of white adipose tissue from human newborns and adult volunteers were estimated. The activity of CAT/mg mitochondrial protein did not change with age, while that of CPT was decreased in the adult. Carnitine content of newborn white adipose tissue was about 26 nmol/g wet weight, much lower than in other organs from human fetuses. Isolated white adipose tissue cells from newborn babies reacted to deoxycarnitine addition by a decrease in respiration; no such effect was observed in adult cells. In addition, the enhancing effect of norepinephrine on oxygen consumption of newborn cells could be further elevated by adding l-carnitine and again this was not observed in adult adipocytes.

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“…Carnitine acetyltransferasc (CAT) was determined as described by Barker et at. [2], The determination of carnitine palmitoyltransferase (CPT) according to N orum [12, see 5 for details] was found not to be very satisfactory. In fact when applied to rat tissue results were very different from those described by H oppel and Tomec [7] using a different method.…”

Section: Methodsmentioning

confidence: 99%