Explain how carbon flux through the pentose phosphate pathway is regulated.

Carbon flux through the pentose phosphate pathway (PPP) is mainly controlled by NADPH on the first enzyme of the irreversible oxidative phase, glucose-6-phosphate dehydrogenase. When [NADPH] increases, it inhibits the enzyme, while low concentrations, which is usually a result of in-creased lipogenesis (the process by which simple sugars are converted to fatty acids) stimulates glucose-6-phosphate dehydrogenase activity. NADPH is also used by cytochrome P450, a monooxygenase that oxidizes the NADPH to NADP+ during the oxidation of fatty acids in the endoplasmic reticulum, where the first reaction places a hydroxyl group onto the omega carbon – this process reduces [NADPH] concentration. Likewise, the maintenance of reduced glu-tathione, a powerful antioxidant also requires NADPHRed via the enzyme glutathione reductase to prevent red blood cells from free-radical damage. This process also decreases [NADPH] concentration