Glycerol from glyceraldehyde

D-Glyceric acid (or D-2,3-dihydroxypropanoic acid C3H604, MW = 125.10) is a hydroxy acid derived from the oxidation of Cl of glycerol or glyceraldehyde to a carboxyl group various phosphorylated derivatives of L-glycerate are important intermediates in glucose metabolism (Fig. 3.5.3). 

Fructose-l,6-diphosphate (FDP) may also be converted into dihydroxyacetone phosphate (DHAP), which is also synthesized from glyceraldehyde-3-phosphate (GAP). The dihydroxyacetone phosphate (DHAP), thus obtained, is converted into glycerol-3-phosphate (G-3-P), in the presence of cytosolic NADH. The latter gives away one phosphate radical to ADP to generate ATP and glycerol (Chart 1). Thus in the above process, one mole of glucose is converted into two moles of pyruvate with a net gain of two moles of ATP [1],... 

Ricinine.—Ricinine (49), the alkaloid of castor bean plants, is derived from nicotinic acid (28) and quinolinic acid (48), and its formation is intimately associated with the pyridine nucleotide cycle cf. ref. 6. Quinolinic acid is built from a C3 fragment that is formed from glycerol via glyceraldehyde and a C4 unit that is related to succinic or aspartic acids. A recent investigation has confirmed this pathway for ricinine (49) and indicated that dihydroxyacetone phosphate lies between glycerol and glyceraldehyde (loss of tritium from C-2 of labelled glycerol). ... 

The glycerol from fat breakdown feeds into the glucose breakdown/synthesis pathways at the level of glyceraldehyde 3-phosphate. It is important, however, to note that the fatty acids themselves cannot yield glucose. They form acetyl CoA, but in humans there is no route back from acetyl CoA to pyruvate. The conversion of pyruvate into acetyl CoA is effectively a one-way valve. Thus, it is easy to convert excess carbohydrate into fat but not the other way round. 

Loss of two hydrogens by glycerol leads to the formation of glyceraldehyde or dihydroxyacetone, depending on whether the two hydrogens are lost from the end or middle position, respectively. 

The simplest carbohydrates, sometimes referred to as monosaccharides, or sugars, are either polyhydroxyaldehydes (aldoses) or polyhydroxyketones (ketoses). They can be derived from polyalcohols (polyols) by oxidation of one carbinol group to a carbonyl group. For example, the simple three-carbon triol, glycerol, can be converted either to the aldotriose, glyceraldehyde, or to the ketotriose, dihydroxyacetone, by loss of two hydrogens (fig. 12.1). 

A different type of reduced sugar is an alditol, in which the aldehyde group of an aldose has been reduced. For example, the alditol produced from D-glucose is D-glucitol (the trivial name is sorbitol). The name of an alditol is obtained by adding -itol to the root of the name of the aldose (except for glycerol, a reduction product of glyceraldehyde). 

Fig. 41 Scheme of the synthesis of L-glyceraldehyde by reduction of D-glyceraldehyde out of the racemic mixture using NADP-dependent glycerol dehydrogenase from Gluconobacter... 

Fig. 23. Proposed active site arrangement of sn-glycerol-3-phosphate dehydrogenase (below), based on secondary structure predicted from the known primary structure, and on comparison with the known tertiary structure of glyceraldehyde-3-phosphate dehydrogenase (above). From the work of Rossmann and colleagues (94).

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