ENERGETICS OF BETA-OXIDATION - REDUCTION POTENTIALS OF GENERAL FATTY ACYL-COA DEHYDROGENASE, ELECTRON-TRANSFER FLAVOPROTEIN, AND FATTY ACYL-COA SUBSTRATES

Google Scholar
  • 15 June 1986
    • journal article
    • research article
    • Vol. 261  (17) , 7733-7741
Abstract
We have determined reduction potentials for porcine mitochondrial general fatty acyl-CoA dehydrogenase (GAD) and electron transfer flavoprotein (ETF) using an anaerobic spectroelectrochemical titration method. Computer stimulation techniques were used to analyze the absorbance data. Nernst plots of the simulated data gave .**GRAPHIC**. = -0.014 V and .**GRAPHIC**. = -0.036 V for ETF and .**GRAPHIC**. = -0.155 V and .**GRAPHIC**. = -0.122 V for GAD. Using these techniques we have also determined a conditional reduction potential of -0.156 V for the chromophore producing fatty acyl-CoA substrate .beta.-2-furylpropionyl-CoA. From this value and our previous determination of the equilibrium constant for the transhydrogenation reaction between .beta.-2-furylpropionyl-CoA and the oxidized substrate crotonyl-CoA (Keq = 10.4), we have determined a reduction potential of -0.126 V for the butyryl-CoA/crotonyl-CoA couple. In light of the structural similarity between butyryl-CoA and octanoyl-CoA, the optimal substrate for GAD, the reduction potential for octanoyl-CoA should be similar to that for butyryl-CoA; i.e. fatty acyl-CoA substrates and GAD are essentially isopotential. The ability of octanoyl-CoA to reduce GAD quantitatively (Keq = 9.0) poses a dilemma in light of the nearly equal reduction potentials. We postulate the stable charge-transfer complex formed between enzyme and optimal product is significantly lower in energy than enzyme and product and thus is responsible for pulling the reaction toward completion.