Section 7. Lipid Metabolism. Fats: fatty acid biosynthesis. 11/04/05. Oxidation of Fatty Acids Other Than Palmitate. Any even number of saturated carbons does not require any additional enzymes. Products are as for palmitate.
Fats: fatty acid biosynthesis
saturated fatty acid the same length.
An isomerase moves it to the 2-position.
Moving the double bond is energy neutral, but one less FADH2 is made because one acyl CoA dehydrogenase step is “skipped.”
As acetyl CoA’s are removed from an unsaturated fatty acid, double bonds move into or near the active sites of the -oxidation cycle enzymes.Double Bonds in Odd-Numbered Positions
General anesthesia: CO2 up, pH down, ketone bodies up.
Volatile acetone formation is non-enzymatic.
The liver normally converts acetyl CoA to ketone bodies that are used by peripheral tissues.
See fig. 22.19Ketone Bodies
This is the committed step in fatty acid biosynthesis.
ATP provides energy.
Biotin is a cofactor.
Two sequential reactions occur in the active site.Activation by Acetyl CoA Carboxylase
biotin-Enz + ATP + HCO3- CO2~biotin-Enz + ADP + Pi
CO2~biotin-Enz + acetyl CoA malonyl CoA + biotin-Enz
Figs. 24-10 and 24-11 (Stryer 4th)
Condensation forms 4 carbon unit on acyl carrier protein (ACP).
Reduction of ketone to hydroxyl by NADPH.
8 acetyl CoA + 7 ATP + 14 NADPH + 6 H+
palmitate + 14 NADP+ + 8 CoA + 6 H2O + 7 ADP + 7Pi
For this reaction, there are 7 (for 7 ATP) + 35 (for 14 NADPH) = 42 ~P equivalents used.
Compare to 26 obtained from the palmitate conversion to acetyl CoA by fatty acyl CoA synthetase and the b-oxidation cycle.
Odd Chain Fatty Acids. The fate of propionyl CoA.
Unsaturated Fatty Acid Oxidation. The role of isomerase.
Next Topic: Membrane lipids.