Nonhomogeneous labeling of liver mitochondrial acetyl-CoA.
The specific activity of carbons 1 and 2 of plasma acetoacetate has been used as a measure of the specific activity of liver mitochondrial acetyl-CoA in tracer studies. To test whether or not acetoacetate actually reflects acetyl-CoA, livers were perfused with a mixture of substrates that are converted to mitochondrial acetyl-CoA: 1 mM lactate, 0.2 mM pyruvate, 0.2 mM acetate, and, where indicated, 0.2 mM octanoate or 0.2 mM alpha-ketoisocaproate. In each experiment, one of these substrates was 13C-labeled. Labeling of mitochondrial acetyl-CoA was assessed by three methods: (i) molar percent enrichment of total tissue acetyl-CoA; (ii) molar percent enrichment of carbons 4 and 5 of tissue citrate, the precursor of which is acetyl-CoA; and (iii) molar percent enrichment of carbons 1 and 2 of perfusate ketone bodies. Nonhomogeneous labeling of liver mitochondrial acetyl-CoA occurred under most conditions, i.e. the enrichments of carbons 4 and 5 of citrate were different from enrichments of carbons 1 and 2 of ketone bodies. Thus, based upon our results obtained in perfused livers, we question the validity of measuring the labeling of carbons 1 and 2 of acetoacetate as a noninvasive probe of liver mitochondrial acetyl-CoA.
Des Rosiers
C
C
Department of Nutrition, University of Montreal, Quebec, Canada.
David
F
F
Garneau
M
M
Brunengraber
H
H
D000085:Acetates / Q000378:metabolism; D000090:Acetoacetates / Q000378:metabolism; D000105:Acetyl Coenzyme A / Q000378:metabolism*; D000818:Animals; D002210:Caprylates / Q000378:metabolism; D002951:Citrates / Q000378:metabolism; D019343:Citric Acid; D007657:Ketone Bodies / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism*; D011773:Pyruvates / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D000085:Acetates; D000090:Acetoacetates; D002210:Caprylates; D002951:Citrates; D007657:Ketone Bodies; D011773:Pyruvates; D019343:Citric Acid; C016635:acetoacetic acid; D000105:Acetyl Coenzyme A