karboxylsyras

Karboxylsyras, or carboxylases, are enzymes that catalyze carboxylation reactions, typically by adding carbon dioxide (CO2) to an organic substrate or by fixing inorganic CO2 into metabolic pathways. Many carboxylases require cofactors to transfer CO2, most commonly biotin in biotin-dependent enzymes, while others rely on metal cofactors such as magnesium.

Two major categories exist. Biotin-dependent carboxylases include acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and methylcrotonyl-CoA carboxylase. These enzymes participate in fatty acid synthesis, replenishment of oxaloacetate for the TCA cycle, and the catabolism of certain amino acids. The second major group comprises RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase), a central enzyme in photosynthetic carbon fixation that operates in chloroplasts and certain bacteria; RuBisCO fixes CO2 to ribulose-1,5-bisphosphate and also catalyzes an oxygenase side reaction that can lead to photorespiration.

Distribution and roles are broad. Carboxylases are found in bacteria, archaea, and eukaryotes. In plants and cyanobacteria, RuBisCO drives CO2 fixation in the Calvin cycle. In animals and many other organisms, biotin-dependent carboxylases contribute to metabolism, including fatty acid synthesis and energy production. Some carboxylases participate in amino acid catabolism and other biosynthetic pathways.

Clinical and industrial relevance is notable. Defects in propionyl-CoA carboxylase or methylcrotonyl-CoA carboxylase cause metabolic disorders such as organic acidemias; biotin deficiency can impair multiple biotin-dependent carboxylases. Biotin supplementation helps in some cases. Biotechnological applications include metabolic engineering to introduce carboxylation steps and to explore carbon fixation strategies.