title: In vivo enzymatic activity of acetylCoA synthetase in skeletal muscle revealed by (13)C turnover from hyperpolarized [1-(13)C]acetate to [1-(13)C]acetylcarnitine.
abstract: BACKGROUND
  Acetate metabolism in skeletal muscle is regulated by acetylCoA synthetase (ACS). The main function of ACS is to provide cells with acetylCoA, a key molecule for numerous metabolic pathways including fatty acid and cholesterol synthesis and the Krebs cycle.
  
  
  METHODS
  Hyperpolarized [1-(13)C]acetate prepared via dissolution dynamic nuclear polarization was injected intravenously at different concentrations into rats. The (13)C magnetic resonance signals of [1-(13)C]acetate and [1-(13)C]acetylcarnitine were recorded in vivo for 1min. The kinetic rate constants related to the transformation of acetate into acetylcarnitine were deduced from the 3s time resolution measurements using two approaches, either mathematical modeling or relative metabolite ratios.
  
  
  RESULTS
  Although separated by two biochemical transformations, a kinetic analysis of the (13)C label flow from [1-(13)C]acetate to [1-(13)C]acetylcarnitine led to a unique determination of the activity of ACS. The in vivo Michaelis constants for ACS were KM=0.35±0.13mM and Vmax=0.199±0.031μmol/g/min.
  
  
  CONCLUSIONS
  The conversion rates from hyperpolarized acetate into acetylcarnitine were quantified in vivo and, although separated by two enzymatic reactions, these rates uniquely defined the activity of ACS. The conversion rates associated with ACS were obtained using two analytical approaches, both methods yielding similar results.
  
  
  CONCLUSIONS
  This study demonstrates the feasibility of directly measuring ACS activity in vivo and, since the activity of ACS can be affected by various pathological states such as cancer or diabetes, the proposed method could be used to non-invasively probe metabolic signatures of ACS in diseased tissue.
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Jessica A M
authors.initials: JA
authors.lastname: Bastiaansen
authors.forename: Tian
authors.initials: T
authors.lastname: Cheng
authors.forename: Mor
authors.initials: M
authors.lastname: Mishkovsky
authors.forename: João M N
authors.initials: JM
authors.lastname: Duarte
authors.forename: Arnaud
authors.initials: A
authors.lastname: Comment
authors.forename: Rolf
authors.initials: R
authors.lastname: Gruetter
mesh_terms: D000106:Acetate-CoA Ligase / Q000378:metabolism*; D000085:Acetates / Q000378:metabolism*; D000108:Acetylcarnitine / Q000378:metabolism*; D000818:Animals; D002247:Carbon Isotopes; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000085:Acetates; D002247:Carbon Isotopes; D000108:Acetylcarnitine; D000106:Acetate-CoA Ligase