Biochemistry - The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

Organization of Metabolism: Catabolic Pathways
Fatty Acid Oxidation

METABOLISM involves an immense variety of Chemical Reactions. Many of these are organized into complex cycles that can sometimes be difficult to follow. Yet, underlying this complexity are logic and order. With few exceptions, metabolic pathways consist of sequential reactions such as those described in chapters 7, 8, and 10 (and summarized in Table 9-1), with each chain of reactions organized to accomplish a specific chemical task.

In this chapter, we will examine some of the primary pathways involved in the Catabolism of Cell/8.html">Nutrients and Cellular components. Anabolic (biosynthetic) reactions will be discussed in subsequent chapters.

The combustion of Hydrocarbons yields substantially more energy than the combustion of most other Organic compounds, so it is hardly surprising that fats—the primary form of nutrient storage in the body—are predominantly hydrocarbon in nature. From an energetic standpoint, the fatty acid components are of the greatest significance. Most aerobic Cells are capable of completely oxidizing Fatty acids to СО₂ and Water through processes that take place within the mitochondrial matrix of Eukaryotic cells.

The site of chemical attack is the oxidized end of the fatty acid. The initial stage is a "priming reaction" in which the fatty acid undergoes a sequence of chemical transformations S1A(a) [see Table 7-2 — Ed.] to form a water-soluble acyl-CoA derivative, a compound in which the α-hydrogens of the fatty acid radicals are "activated" [Equation (9-1)]:

Class="center">

This reaction is catalyzed by acetate thiokinase [Equation (7-30)] and other acyl-CoA synthetases—Enzymes that activate fatty acids. There are at least Two Types of such enzymes: some are specific for medium-length carbon chains (ranging from 4 to 12 carbon atoms), while others target longer chains. Mitochondria also contain acyl-CoA synthetases [1] capable of cleaving GTP to GDP and P_i, in which case The sequence of reactions is SlA(y).

Major Types of Metabolic Reactions