CHAPTER 3
Comparative Mechanisms for Fatty Acid Oxidation
P. K. STUMPF and G. A. BARBER
Department of Biochemistry, University of California, Davis, and
Department
of Biochemistry, University of California,
Berkeley, California
I. Energetics of Fatty Acid Oxidation
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II. Mechanism for Release of the Potential Energy in Fatty Acids
.
.
77
A. Activation Step
78
B. Formation of the Ethylenic Group
82
C. Second Dehydrogenation Step
87
D. Thiolytic Cleavage
89
III. Non-Energy-Yielding Systems
90
A. Lipoxidase
90
B. Fatty Acid Peroxidase
91
IV. Mechanism of Odd-Chain Fatty Acid Oxidation
92
A. Methylmalonate Pathway
93
B. ß-Hydroxypropionate Pathway
93
C. Bacterial Pathway
94
V. Fatty Acid Oxidation — Comparative Aspects
94
A. Anaerobic Bacteria
94
B. Aerobic Bacteria
98
C. Fungi
99
D. Higher Plants and Animal Tissues
101
VI. Conclusion
102
References
103
As substrates fatty acids are unique in biological systems since they
are the most highly reduced compounds that are completely available
as energy sources. Readily synthesized from carbohydrates and stored
mainly as triglycerides, on combustion they release more energy than
any other general type of foodstuff. For example, on combustion 1 gm.
of carbohydrate will yield 4200 cal., 1 gm. of protein, 5600 cal., and 1
gm. of fat, 9300 cal. It is therefore of considerable interest to examine
the mechanisms found in organisms for the oxidation of fats and the
trapping of large amounts of energy thereby released. No attempt will
be made to review the very large literature on the occurrence and structure of fatty acids in different phyla nor their biosynthesis.
75