Glucose galactose conversion

Many aliphatic aldehydes exist primarily as hemiacetals in alcoholic solvents. It has been well understood for many years47 that the actual reducible species, or electrophore , in such media is not the hemiacetal but rather the small amount of the carbonyl compound itself (actually a hydrogen-bonded complex see above) present at equilibrium. Thus reduction is kinetically controlled that is, the overall rate of reduction is governed by the rate of conversion of the hemiacetal to the aldehyde. More recently, this has been confirmed and studied for formaldehyde and acetaldehyde in water at different pH levels48 and the kinetics of the reduction process have been studied for glucose, galactose and lactose49. 

Conversion of all hexose monomers, meaning glucose, galactose, and mannose. 

Through what does galactose conversion to glucose proceed ... 

Biochemical epimerizcUum at certain asymmetric centers has been discovered relatively recently. An example is glucose galactose the coenzyme is uridine diphosphate, whose reactions will be discussed in another context (cf. Chapt. XVII-4). Among the pentoses, there is the conversion of ribvilose 5-phosphate to xylulose 5-phosphate (epimerization at C-3). 

In all plants and most animals, L-ascorbic acid is produced from D-glucose (4) and D-galactose (26). Ascorbic acid biosynthesis in animals starts with D-glucose (4). In plants, where the biosynthesis is more compHcated, there are two postulated biosynthetic pathways for the conversion of D-glucose or D-galactose to ascorbic acid. 

Figure 20-6. Pathway of conversion of (A) galactose to glucose in the liver and (B) glucose to lactose in the lactating mammary gland.

Most of our present information on the conversion of galactose to glucose has come from the study of microorganisms, particularly the yeast Saccharomyces fragilis. However, there is ample evidence that the same metabolic paths are followed in mammalian tissue. 

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