3. MECHANISMS FOR FATTY ACID OXIDATION
77
it is now possible to calculate the maximum amount of energy that may
be trapped by known mechanisms of ^-oxidation in the cell.
Step I:
Palmitate —> 8 Acetyl-CoA + 14 electron pairs
7 electron pairs —* Flavin system (7X2) = 14 ^
7 electron pairs -> DPN+ system (7 X 3) = 21 ~
Total = 35 ~
One —' is required for the activation of palmitate by the ATP-CoA system* and must be deducted from the total synthesized to give 34 ^.
Step II:
8 Acetyl-CoA + 16 0 2 -* 16 C0 2 + 8 H 2 0 + 8 CoA
In this step acetyl-CoA is presumed to be degraded through the Krebs
cycle to C0 2 and water. Assuming a P/O ratio of 3 for the phosphorylative oxidation of acetyl-CoA, 32 χ 3 = 96 ^ are formed. In summation:
Step I = 34 ~
Step II = 96 ~
Total = 130 ~
^m x *» - »*
Thus in the complete oxidation of a typical long chain fatty acid
such as palmitate, approximately 39% of total available energy is trapped
by known systems and suggests the potential importance of fatty acids
as sources of useful energy. Whether or not the electron pairs and the
thiol ester bonds are channeled as assumed above is however difficult
to ascertain.
II. Mechanism for Release of the Potential Energy in Fatty Acids
The calculations made in Section I are based on the classical sequence of /^-oxidation. It is therefore worthwhile to examine in some
detail the five steps that lead from the initial activation of a fatty acid
molecule to the release of an acetyl-CoA unit and then survey the
position of this mechanism in other tissues. Figure 1 summarizes the
various steps.
* Abbreviations used in this chapter: CoA, coenzyme A; AMP, adenosine monophosphate; ADP, adenosine diphosphate; ATP, adenosine triphosphate; GSH, glutathione; P i? inorganic phosphate; PP, pyrophosphate; DPN+, diphosphopyridine
nucleotide; DPNH, reduced diphosphopyridine nucleotide; ETF, electron transfer
flavoprotein; FAD, flavin adenine dinucleotide; TCA, tricarboxylic acid; —, highenergy bond.
77
it is now possible to calculate the maximum amount of energy that may
be trapped by known mechanisms of ^-oxidation in the cell.
Step I:
Palmitate —> 8 Acetyl-CoA + 14 electron pairs
7 electron pairs —* Flavin system (7X2) = 14 ^
7 electron pairs -> DPN+ system (7 X 3) = 21 ~
Total = 35 ~
One —' is required for the activation of palmitate by the ATP-CoA system* and must be deducted from the total synthesized to give 34 ^.
Step II:
8 Acetyl-CoA + 16 0 2 -* 16 C0 2 + 8 H 2 0 + 8 CoA
In this step acetyl-CoA is presumed to be degraded through the Krebs
cycle to C0 2 and water. Assuming a P/O ratio of 3 for the phosphorylative oxidation of acetyl-CoA, 32 χ 3 = 96 ^ are formed. In summation:
Step I = 34 ~
Step II = 96 ~
Total = 130 ~
^m x *» - »*
Thus in the complete oxidation of a typical long chain fatty acid
such as palmitate, approximately 39% of total available energy is trapped
by known systems and suggests the potential importance of fatty acids
as sources of useful energy. Whether or not the electron pairs and the
thiol ester bonds are channeled as assumed above is however difficult
to ascertain.
II. Mechanism for Release of the Potential Energy in Fatty Acids
The calculations made in Section I are based on the classical sequence of /^-oxidation. It is therefore worthwhile to examine in some
detail the five steps that lead from the initial activation of a fatty acid
molecule to the release of an acetyl-CoA unit and then survey the
position of this mechanism in other tissues. Figure 1 summarizes the
various steps.
* Abbreviations used in this chapter: CoA, coenzyme A; AMP, adenosine monophosphate; ADP, adenosine diphosphate; ATP, adenosine triphosphate; GSH, glutathione; P i? inorganic phosphate; PP, pyrophosphate; DPN+, diphosphopyridine
nucleotide; DPNH, reduced diphosphopyridine nucleotide; ETF, electron transfer
flavoprotein; FAD, flavin adenine dinucleotide; TCA, tricarboxylic acid; —, highenergy bond.