carboxilasa

Carboxilasa, or carboxylase, is a broad class of enzymes that catalyze the addition of a carboxyl group to an organic substrate, a reaction known as carboxylation. Most biochemically characterized carboxylases rely on bicarbonate or CO2 as the carbon source and often use ATP to activate the process. Many are biotin-dependent and employ a biotin prosthetic group that acts as a carrier for the carboxyl group between enzyme active sites.

Among the best-known examples are biotin-dependent carboxylases. Pyruvate carboxylase, located in mitochondria, converts pyruvate to oxaloacetate in an ATP-driven carboxylation, contributing to anaplerosis of the tricarboxylic acid cycle and to gluconeogenesis in the liver. Acetyl-CoA carboxylase, found in the cytosol, carboxylates acetyl-CoA to produce malonyl-CoA, a key committed step in fatty acid synthesis. Propionyl-CoA carboxylase, also mitochondrial, converts propionyl-CoA to D-methylmalonyl-CoA, a step in the metabolism of certain amino acids and fats. Other carboxylases include 3-methylcrotonyl-CoA carboxylase and methylcrotonyl-CoA carboxylase, which participate in catabolic pathways of branched-chain amino acids and odd-chain lipids.

Physiological roles vary by enzyme, but collectively carboxylases regulate energy metabolism, lipid synthesis, and amino acid catabolism. They are often tightly regulated by cellular energy status, allosteric effectors, and post-translational modifications. Defects in specific carboxylases can cause metabolic disorders; for example, biotinidase deficiency affects multiple biotin-dependent carboxylases, while propionic acidemia arises from propionyl-CoA carboxylase deficiency.

In summary, carboxilasa encompasses a family of enzymes essential for introducing carboxyl groups into substrates, with diverse substrates, cofactors, and cellular functions.