karboksylaatio

Karboksylaatio, or carboxylation, is a chemical reaction in which a carboxyl group (-COOH) is introduced into a molecule. In biological systems this typically involves the incorporation of carbon dioxide (CO2) or bicarbonate (HCO3-) into an organic substrate, catalyzed by carboxylase enzymes. Many carboxylases require cofactors such as biotin, ATP, or metal ions to activate the substrate and facilitate CO2 transfer.

In plants and other photosynthetic organisms, carboxylation is a central step in carbon fixation. The enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) carboxylates ribulose-1,5-bisphosphate to form two molecules of 3-phosphoglycerate, a key stage of the Calvin cycle. In C4 plants and some bacteria, phosphoenolpyruvate carboxylase (PEP carboxylase) carboxylates PEP to oxaloacetate, concentrating CO2 for RuBisCO and reducing photorespiration. In animals and many microbes, pyruvate carboxylase converts pyruvate to oxaloacetate, supporting gluconeogenesis and replenishment of TCA cycle intermediates (anaplerosis). Acetyl-CoA carboxylase forms malonyl-CoA, a committed substrate in fatty acid synthesis.

Karboksylaatio is essential for energy metabolism, biosynthesis, and carbon cycling. Its regulation influences metabolic flux between carbohydrate, lipid, and amino acid pathways, and it has significance in agriculture, biotechnology, and environmental carbon management.