Dehydrogenation of succinic acid

The biological dehydrogenation of succinic acid described in Section 5 8 is 100% stereoselective Only fumaric acid which has a trans double bond is formed High levels of stereoselectivity are characteristic of enzyme catalyzed reactions... 

Although enzymes catalyze only certain reactions or certain types of reaction, they are still subject to interference. When the activated complex is formed, the substrate is adsorbed at an active site on the enzyme. Other substances of similar size and shape may be adsorbed at the active site. Although adsorbed, they will not undergo any transformation. However, they do compete with the substrate for the active sites and slow down the rate of the catalyzed reaction. This is called competitive inhibition. For example, the enzyme succinic dehydrogenase will specifically catalyze the dehydrogenation of succinic acid to form fumaric acid. But other compounds similar to succinic acid will competitively inhibit the reaction. Examples are other diprotic acids such as malonic and oxalic acids. Competitive inhibition can be reduced by increasing the concentration of the substrate relative to that of the interferent so that the majority of enzyme molecules combine with the substrate. 

Dehydrogenation of succinic acid into fumaric acid is catalyzed by succinate dehydrogenase, a mitochondrial FAD-enzyme (Singer and Kearney, 1963). 

Oxidation may take place by a modified tricarboxylic acid cycle in which the production of CO2 is coupled to the synthesis of NADPH and reduced ferredoxin, and the dehydrogenation of succinate to fumarate is coupled to the synthesis of reduced menaquinone. This pathway is used, for example, by Desulfuromonas acetoxidans and in modified form by... 

Reactions analogous to those of the TCA-cycle are found in the biosynthesis of leucine and lysine (Fig. 4). Similarly, the sequence of reactions represented by the dehydrogenation of succinate by a fla-voenzyme, followed by hydration of fumarate to ma-late, then dehydrogenation of malate by a NAD-linked dehydrogenase, finds a counterpart in the initial stages of fatty acid degradation (see). 

The onward metabohsm of succinate, leading to the regeneration of oxaloacetate, is the same sequence of chemical reactions as occurs in the P-oxidation of fatty acids dehydrogenation to form a carbon-carbon double bond, addition of water to form a hydroxyl group, and a hirther dehydrogenation to yield the oxo- group of oxaloacetate. 

Researchers have reported that under anaerobic conditions, the oxidation of phosphoric acid in the mitochondria of plants became weakened and reduction potential increased. That means the ratio of NADH and NAD-r increased and ADP transformed to ATP. This caused the dehydrogenation activity of succinic semialdehyde dehydrogenase to decrease, and resulted in weakening the reaction of succinic semialdehyde dehydrogenase to form succinate this is beneficial to the accumulation of GABA in tea leaves. Sawai et al. further reported that the amount of... 

---