Thiamine pyrophosphate as a decarboxylation cofactor
Thiamine (vitamin B1) is biologically active mainly as thiamine pyrophosphate (TPP, also called thiamine diphosphate). The reactive part is the thiazolium ring, whose carbon between sulphur and nitrogen can lose a proton to form a carbanion that attacks carbonyl groups. This chemistry lets TPP act as a cofactor for enzymes that cleave carbon-carbon bonds next to a keto group, the oxidative decarboxylations central to releasing energy from carbohydrate.
Two pivotal complexes depend on it: pyruvate dehydrogenase, which links glycolysis to the citric acid cycle by converting pyruvate to acetyl-CoA, and alpha-ketoglutarate dehydrogenase, a step within the cycle itself. Transketolase in the pentose phosphate pathway and branched-chain ketoacid dehydrogenase also require TPP, so thiamine status touches both energy production and biosynthesis.
Why thiamine-dependent tissues fail first
Because the brain and heart rely heavily on aerobic glucose metabolism, they are among the first tissues affected when thiamine is scarce. Classical deficiency presents as beriberi (with cardiac and neurological forms) and, in the context of heavy alcohol use or malnutrition, as Wernicke encephalopathy. The body stores relatively little thiamine, so depletion can develop over weeks rather than months.
This is general educational information, not medical advice. Suspected thiamine deficiency, particularly with neurological symptoms, is a clinical situation that should be assessed and treated by a qualified healthcare professional rather than self-managed.