The Modification of Carboxyl Groups

The selective modification of carboxyl groups was the subject of one of the early attempts to adapt organic chemistry to the systematic study of the relationship between structure and function in proteins. Active-site directed reactions with reactive epoxy functional groups have proved useful in several studies of the role of carboxyl groups in proteins. The modification of an essential carboxyl group in pancreatic phospholipase A₂ by 5-ethyl-5-phenylisoxazolium-3-sulfonate has been reported. The use of carbodiimide-mediated modification of carboxyl functional groups in proteins is by far the most widely used method for the study of such functional groups. Diazo compounds have proved useful for some time in the esterification of the carboxyl groups of proteins. The enzymatic methylation of protein carboxyl groups has been reported. Raftery and co-workers used triethyloxonium fluoroborate to modify the ß-carboxyl groups of an aspartic residue essential for the enzymatic activity of lysoszyme.