Ojuka 2015 Abstract MiPschool Cape Town 2015

Use of malate or carnitine as co-substrates for assessment of fatty acid oxidation.

Link:

Ojuka E (2015)

Event: MiPschool Cape Town 2015

Acylcarnitines when converted to acyl –CoA in the mitochondrial matrix are a major source of ATP after oxidation. Their oxidation process, termed β-oxidation, runs through four sequential enzymes namely: acyl-CoA dehydrogenase, 2-enoyl-CoA hydratase, L-3-hydroxyacyl- CoA dehydrogenase, and 3-ketoacyl-CoA thiolase [1]. Acyl-CoA dehydrogenases transfer single electrons to electron transferring flavoprotein (ETF) [2] which donates electrons directly to the ubiquinone (Q) pool in the mitochondrial inner membrane. Hydroxyacyl-CoA dehydrogenase transfers electrons to NAD+ and the reduced NADH is oxidized by complex I. The end product of β-oxidation, acetyl-CoA, condenses with oxaloacetate to form citrate which is oxidized by the Krebs cycle. Oxidation of fatty acylcarnitines therefore contributes to OXPHOS and ATP production by donating electrons at various points of the electron transfer-pathway.

To assess oxidation of acylcarnitines under various experimental conditions, scientist often measure oxygen consumption in isolated mitochondria, permeabilized cells, or tissues in an oxygraph using a variety of substrate combinations including palmatoylcarnitine in combination with carnitine or malate. Use of palmatoylcarnitine alone yields low oxygen flux rates and is not responsive to ADP, oligomycin or uncouplers. These observations are attributed to a low CoA/ palmatoylCoA ratio which inactivates 3-ketoacyl-CoA thiolase and slows down or stops β-oxidation. Use of palmatoylcarnitine in combination with carnitine or malate increase State 2 respiration (oxygen consumption with substrate without addition of ADP) and are responsive to ADP, oligomycin and uncouples -- but to different degrees. The increase in oxygen flux rates after ADP or uncoupler addition is explained by the increased CoA/palmatoylCoA ratio which favours β-oxidation. The differences in response to ADP and uncoupler is probably due the fact that oxidation of palmitoylcarnitine in the presence of carnitine transfers electrons to the ETS without involving the Krebs cycle whereas oxidation of palmitoylcarnitine and malate does [3].

• O2k-Network Lab: ZA Cape Town Smith J, ZA Cape Town Ojuka EO

Labels: MiParea: Respiration 

Preparation: Permeabilized cells, Permeabilized tissue, Isolated mitochondria  Enzyme: Complex I 

Coupling state: LEAK, OXPHOS, ET 

HRR: Oxygraph-2k 

Affiliations

Inst South Africa Newlands, ESSM UCT Dept Human Biol Sports Sc, Univ Cape Town. - edward.ojuka@uct.ac.za

References

1. Kim JJ, Battaile KP (2002) Burning fat: the structural basis of fatty acid beta-oxidation. Curr Opin Struct Biol 12:721-28.
2. MacKenzie J, Pedersen L, Arent S, Henriksen A (2006) Controlling electron transfer in Acyl-CoA oxidases and dehydrogenases: a structural view. J Biol Chem 281:31012-20.
3. Perevoshchikova IV, Quinlan CL, Orr AL, Gerencser AA, Brand MD (2013) Sites of superoxide and hydrogen peroxide production during fatty acid oxidation in rat skeletal muscle mitochondria. Free Radic Biol Med 61:298-309.