Glyceric aldehyde, oxidation

Figure 17-3. Mechanism of oxidation of giyceraldehyde 3-phosphate. (Enz, glycer-aldehyde-3-phosphate dehydrogenase.) The enzyme is inhibited by the— 5H poison iodoacetate, which is thus abie to inhibit glycolysis. The NADH produced on the enzyme is not as firmly bound to the enzyme as is NAD. Consequently, NADH is easily displaced by another molecule of NAD". ...

Furthermore, a base-catalyzed transformation by OH from the reaction medium between glycerate and hydroxypyruvate aldehyde (or hydroxypyruvic acid) could be excluded, while hydroxyacetone and glyceraldehyde interconversion was possible (Scheme 11.11). The existence of two major routes, of which hydroxyacetone and glyceric aldehyde are the primary oxidation products and glycolic and oxalic acid are the end-members, respectively, is now firmly established. Clearly, rapid oxidation of glyceraldehydes favors glyceric acid rather than hydroxyacetone formation. 

The product of this metabolic sequence, pyruvate, is a metabolite of caitral importance. Its fate depends upon the conditions within a cell and upon the type of cell. When oxygen is plentiful pyruvate is usually converted to acetyl-coenzyme A, but under anaerobic conditions it may be reduced by NADH + H+ to the alcohol lactic acid (Fig. 10-3, step h). This reduction exactly balances the previous oxidation step, that is, the oxidation of glycer-aldehyde 3-phosphate to 3-phospho-glycerate (steps a and b). With a balanced sequence of an oxidation reaction, followed by a reduction reaction, glucose can be converted to lactate in the absence of oxygen, a fermentation process. The lactic acid fermentation occurs not only in certain bacteria but also in our own muscles under conditions of extremely vigorous exercise. It also occurs continuously in some tissues, e.g., the transparent lens and cornea of the eye. 

Figure 2.2.12 Reaction network of glycerol oxidation (GLY, glycerol DHA, dihydroxyace-tone GLA, glyceric aldehyde GLS, glyceric acid HBT, hydroxypyruvic acid MOS, mesoxalic acid TS, tartronic acid GOX, glyoxal GOS, glycolic acid GYS, glyoxylic acid OS, oxalic acid).

Dastoor Z, Dreyer JL (2001) Potential role of nuclear tr anslocation of glycer aldehyde-3-phosphate dehydrogenase in apoptosis and oxidative str ess. J Cell Sci 114 Pt 9 1643—1653. 

Witzemann, E J, The isolation of crystalline DL-glyceric aldehyde from a syrup obtained by the oxidation of glycerol, J. Am. Chem. Soc., 36, 2223-2234, 1914. 

At this point, to complete the subject of the radical oxidation of substituted carboxaldehydes, mention should be made of the findings concerning glyceric aldehyde [43], In the aqueous phase, the oxidation of this compound is a chain reaction. The accumulation of intermediate products such as glyceride and glycolic acids at the same time as acetic and formic acids and C02 indicates that this aldehyde has two reactive oxidation sites, i.e. the carbonyl group and the carbon a to this group. 

The preceding reactions yield two molecules of NADPH and one molecule of ribose 5-phosphate for each molecule of glucose 6-phosphate oxidized. However, many cells need NADPH for reductive biosyntheses much more than they need ribose 5-phosphate for incorporation into nucleotides and nucleic acids. In these cases, ribose 5-phosphate is converted into glycer-aldehyde 3-phosphate and fructose 6-phosphate by transketolase and transaldolase. These enzymes create a reversible link between the pentose phosphate pathway and glycolysis by catalyzing these three successive reactions. 

Further electrolysis of glyceric aldehyde gave the ordinary oxidation products, and, as in the case of glycol, a substance closely related to ordinary glucose. Bartoli and Papasogli repeated these experiments, varying the material of the electrodes, and obtained the following results ... 

The synthesis of 24 (Fig. 16) started with the Grignard addition to glycer-aldehyde 30 which furnished 31 with good anti-selectivity. Mitsunobu reaction, diastereomer separation by crystallization and acetonide hydrolysis gave 32, which was converted into 33 by oxidation and into 24 after hydrazinolysis. 

A coupled enzyme system can also be used. The glycer-aldehyde-3-phosphate formed is converted to dihydroxy-acetone phosphate by triosephosphate isomerase and this is followed by reduction by glycerol phosphate dehydrogenase. The oxidation of NADH in this last stage is measured spectrophotometrically. 

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