esterasi

Esterases are a broad group of enzymes that catalyze the hydrolysis of ester bonds in a wide variety of substrates, yielding an alcohol and a carboxylic acid. They are part of the hydrolase enzyme class (EC 3.1) and include several families such as cholinesterases, carboxylesterases, and arylesterases. While they share the general mechanism of nucleophilic attack on the carbonyl carbon, esterase substrates are typically small, and they differ from lipases, which prefer long-chain, water-insoluble esters.

Most esterases are serine hydrolases that use a catalytic triad (serine, histidine, and an aspartate or glutamate) to activate a bound water molecule for ester hydrolysis. The reaction proceeds via acyl-enzyme intermediates in many cases, followed by hydrolysis to release alcohol and acid. Some esterases operate via different catalytic strategies but retain the same overall chemistry.

In humans, esterase activity is widespread. Liver carboxylesterases (CES1 and CES2) metabolize many drugs and xenobiotics, and plasma enzymes such as acetylcholinesterase and butyrylcholinesterase regulate nerve signaling and drug clearance. Esterases are also found in microbes, plants, and insects, where they participate in metabolism, detoxification, and sometimes insecticide resistance.

Biotechnologically, esterases provide tools for drug development, stereoselective hydrolysis or synthesis, and environmental bioremediation. Clinically, cholinesterase inhibitors are used therapeutically (e.g., in Alzheimer's disease or myasthenia gravis) and accurate esterase activity measurements help diagnose poisoning or monitor exposure to organophosphates. Assays include p-nitrophenyl ester substrates for general esterase activity and Ellman-type assays for cholinesterases.