Issue link: https://wardsworld.wardsci.com/i/1493955
3 Oxidoreductases, which catalyze reactions involving elec- tron transfer, play an important role in cellular respiration and energy production. Some of these enzymes participate in the process of oxidative phosphorylation, whereby the energy released by the oxidation of carbohydrates and fats is directed to the synthesis of adenosine triphosphate (ATP) and thus made directly available for energy-requiring reactions. Most oxidoreductases require prosthetic groups or coenzymes as intermediate electron carriers. These coenzymes include the flavin nucleotides, the pyridine nucleotides, heme, and vari- ous metal ions (for example, iron, copper, and molybdenum). Some oxidoreductases, termed the oxygenases, catalyze the direct incorporation of oxygen into their substrate. Oxidases are enzymes that utilize molecular oxygen as an electron acceptor, whereas dehydrogenases remove hydrogen atoms from their substrates and transfer them to an acceptor other than oxygen. For example, glucose oxidase catalyzes the chemical process shown in reaction (1). Transferases catalyze the transfer of a particular chemical group from one substance to another. The kinases constitute an important subclass of this group, and they catalyze the phosphorylation of their substrates by transferring a phosphate group, usually from ATP, thereby activating an otherwise meta- bolically inert compound for further transformations. Transami- nases require pyridoxal phosphate or pyridoxamine phosphate, derivatives of vitamin B6, as a coenzyme. Chemical processes catalyzed by transaminases may be represented by reaction (2). (1) Enzyme (continued) + ward ' s science (2) (3) Hydrolases catalyze the hydrolysis of numerous chemical substances. For example, proteinases and peptidases catalyze the hydrolysis of proteins, nucleases catalyze the hydrolysis of nucleic acids, amylases catalyze the hydrolysis of starch, lipases catalyze the hydrolysis of fats, and phosphatases catalyze the hydrolysis of phosphate esters. Many hydrolases are secreted by the stomach, pancreas, and intestine for the digestion of foods. Others participate in more specialized cellular functions. For example, cholinesterase, which catalyzes the hydrolysis of acetylcholine, as shown in reaction (3), plays an important role in the transmission of nervous impulses.