ABSTRACT
During more long-term fasting, the brain's demand for glucose is reduced by its adaptation to the use of ketone bodies rather than glucose as its preferred energy substrate (see 'Ketone body synthesis' below). Gluconeogenic activity is also raised in poorly controlled diabetes mellitus and in the hypermetabolic phase of the trauma response. Although the initial reaction of gluconeogenesis occurs in the mitochondrion, much of the pathway, apart from three energetically unfavorable steps, is simply a reversal of the glycolytic pathway. The use of amino acids as substrates for gluconeogenesis requires the removal of the
Fig. 4. The pentose phosphate pathway. GSH, reduced glutathione (glutamylcysteinylglycine); GSSG, oxidized glutathione; H2O2, hydrogen peroxide; PPP, pentose phosphate pathway.
