Gluconeogenesis energy requirements

Summary of the reactions of glycolysis and gluconeogenesis, showing the energy requirements of gluconeogenesis. 

The energy supply required by cirrhotic patients is achieved by mobihzing fats the patient s fatty tissue is reduced and body weight decreases the continuing energy requirement is met by the breakdown of muscle proteins with the result that amino adds are formed, which in turn are used for gluconeogenesis in the liver. Catabolism increases and leads to muscular atrophy, which is known as wasting syndrome. (29, 32, 62, 86, 104, 116, 117, 126)... 

E. Energy requirements for gluconeogenesis 1. From pyruvate (see Figures 5-25 and 5-26)... 

Fig. 31.1. Glycolysis and gluconeogenesis in the hver. The gluconeogenic pathway is almost the reverse of the glycolyrtic pathway, except for three reaction sequences. At these three steps, the reactions are catalyzed by different enzymes. The energy requirements of these reactions differ, and one pathway can be activated while the other is inhibited.

There are two unusual aspects to the regulation of gluconeogenesis. The first step in the reaction, the formation of oxaloacetate from pyruvate, requires the presence of acetyl-CoA. This is a check to make sure that the TCA cycle is adequately fueled. If there s not enough acetyl-CoA around, the pyruvate is needed for energy and gluconeogenesis won t happen. However, if there s sufficient acetyl-CoA, the pyruvate is shifted toward the synthesis of glucose. 

Since much less glucose is required by the brain, the rate of gluconeogenesis falls and hence the rate of protein degradation falls. In the obese, the energy provided from the oxidation of glncose that has been provided by amino acids from protein degradation is as little as 5% of the total (it is much higher in the lean see below). 

The muscles themselves are not capable of gluconeogenesis. Nor would this be useful, as gluconeogenesis requires much more ATP than is supplied by glycolysis. As O2 deficiencies do not arise in the liver even during intensive muscle work, there is always suf -dent energy there available for gluconeogenesis. 

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