There is an alternative pathway for the conversion of glucose 6-phosphate to fructose 6-phosphate, the pentose phosphate pathway (sometimes known as the hexose monophosphate shunt), shown in Figure 5.14.
Overall, the pentose phosphate pathway produces 2 mol of fructose 6-phosphate, 1 mol of glyceraldehyde 3-phosphate and 3 mol of carbon dioxide from 3 mol of glucose 6-phosphate, linked to the reduction of 6 mol of NADP+ to NADPH. The sequence of reactions is as follows:
This is the pathway for the synthesis of ribose for nucleotide synthesis (section
9.2.2); more importantly, it is the source of about half the NADPH required for fatty acid synthesis (section 5.6.1); tissues that synthesize large amounts of fatty acids have a high activity of the pentose phosphate pathway. As discussed in section 126.96.36.199, the pentose phosphate pathway is also important in the respiratory burst of macrophages that are activated in response to infection.
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