Glucose maintaining supplies

Another yeast reductase, Aralp, overexpressed in Escherichia coli, has been used to carry out the DYRKR of 3-oxo-4-phenyl-(3-lactam rac-136. The biotransformation was likewise conducted under fermentation conditions, at 32°C, with a constant supply of oxygen and glucose, maintaining the pH at 7 throughout the reaction (Scheme 57.41). 

Individual tissues have specific roles in maintaining a constant supply of glucose and energy for the whole organism. 

A few hours after eating, the supply of easily available nutrients has been used up and stores must be mobilized to maintain relatively constant supplies of energy and glucose (Fig. 17-7). Insulin levels drop and glucagon levels rise. Because of the increased glucagon levels, cAMP levels rise and regulated proteins become more phosphorylated. 

The CNS is not the only vulnerable tissue as red cells also rely upon a constant supply of glucose to maintain structure and function. Because they lack mitochondria, and therefore the mechanism to produce ATP via oxidative phosphorylation, RBCs are entirely dependent upon anaerobic glucose metabolism to synthesize ATP through substrate level phosphorylation. 

The concentration of glucose in the blood is maintained as a balance between rates of glucose utilisation and glucose supply and changes in one or both of these can lead to hypoglycaemia. Three situations are considered. 

The plasma ketone body level increases rapidly in starvation in pregnancy, which is important in preventing hypoglycaemia in the mother and thus maintaining a supply of glucose for the developing foetus (Chapter 19). 

By contrast, acetyl CoA does not have anaplerotic effects in animal metabolism. Its carbon skeleton is completely oxidized to CO2 and is therefore no longer available for biosynthesis. Since fatty acid degradation only supplies acetyl CoA, animals are unable to convert fatty acids into glucose. During periods of hunger, it is therefore not the fat reserves that are initially drawn on, but proteins. In contrast to fatty acids, the amino acids released are able to maintain the blood glucose level (see p. 308). 

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