Pentosofosfaattireitti

Pentosofosfaattireitti, also known as the pentose phosphate pathway (PPP), is a metabolic pathway parallel to glycolysis. It plays a crucial role in cellular metabolism by generating NADPH and producing pentose sugars. This pathway is essential for various cellular processes, including reductive biosynthesis and the detoxification of reactive oxygen species. The PPP consists of two main phases: the oxidative phase and the non-oxidative phase.

The oxidative phase, which is irreversible, begins with glucose-6-phosphate. Through a series of enzymatic reactions, it produces NADPH and ribulose-5-phosphate. This phase is particularly important for cells that require a significant amount of NADPH, such as red blood cells and cells involved in lipid synthesis. The NADPH produced acts as a reducing agent, essential for anabolic reactions and for protecting cells against oxidative stress.

The non-oxidative phase is a reversible set of reactions that interconverts various sugar phosphates. It can convert pentose phosphates, such as ribose-5-phosphate (a precursor for nucleotide and nucleic acid synthesis), into glycolytic intermediates like fructose-6-phosphate and glyceraldehyde-3-phosphate. This allows the pathway to connect with glycolysis and can also be used to generate pentose phosphates when needed, even if the oxidative phase is not active. The pentose phosphate pathway is thus a flexible metabolic route that supports fundamental cellular functions.