transketolaasi

Transketolase is an enzyme that plays a crucial role in the pentose phosphate pathway. This metabolic pathway is responsible for generating NADPH and producing precursors for nucleotide biosynthesis. Transketolase specifically catalyzes the reversible transfer of a two-carbon fragment from a ketose donor to an aldose acceptor. Its primary function in the pentose phosphate pathway is to convert fructose-6-phosphate and glyceraldehyde-3-phosphate into sedoheptulose-7-phosphate and glyceraldehyde-3-phosphate, or alternatively, into erythrose-4-phosphate and xylulose-5-phosphate.

The enzyme requires thiamine pyrophosphate (TPP) as a cofactor, which is derived from vitamin B1 (thiamine). TPP acts as the nucleophile in the reaction, forming a covalent intermediate with the donor sugar. A deficiency in thiamine can therefore impair transketolase activity, leading to reduced production of NADPH and potentially affecting cellular redox balance and nucleotide synthesis. Transketolase is found in the cytoplasm of cells across various organisms, from bacteria to humans. Its activity is also important in the Calvin cycle of photosynthesis, where it participates in carbon fixation. The enzyme's significance extends to clinical diagnostics, as its activity can be measured in red blood cells as an indicator of thiamine status.