MONOCLONAL ANTIIDIOTYPIC ANTIBODIES AS FUNCTIONAL INTERNAL IMAGES OF ENZYME ACTIVE-SITES - PRODUCTION OF A CATALYTIC ANTIBODY WITH A CHOLINESTERASE ACTIVITY

Monoclonal antibody 9A8 was selected by immunizing mice with AE-2, a m onoclonal antibody directed against the active site of acetylcholinest erase. In accordance with the idiotypic network theory, monoclonal ant i-idiotypic antibody 9A8 displayed internal-image properties of the or iginal immunogen, the acetylcholinesterase active site. Hydrolysis of acetylthiocholine and related esters of thiocholine by 9A8 follows sat uration kinetics and kinetic parameters were determined. The hydrolyti c activity is characterized by a lowered k(cat) value (81 s-1) and an increased K(m) value (0.6 mM) when compared with the original enzyme. However, the rate acceleration (k(cat)/k(uncat) = 4.15 x 10(8)) remain s higher than for the esterase activities usually described for cataly tic antibodies directed against transition-state analogs. The 9A8 acti vity exhibits a relaxation of specificity toward both substrates and i nhibitors. This specificity does not correspond to a known enzymatic a ctivity. The anti-idiotypic approach should be valuable for producing different structural and functional copies of the same enzyme active s ite. This should allow further insights into structure-activity relati onships. Furthermore, use of chemically modified enzymes as immunogens may result in anti-idiotypic antibodies with catalytic activities not found in the native enzymes.