A STRUCTURAL AND KINETIC COMPARISON OF PROTOONCOGENIC AND ONCOGENIC NEU HOLO-RECEPTORS EXPRESSED IN INSECT CELLS

The proto-oncogenic and oncogenic forms of the rat neu receptors were expressed in the baculovirus system to characterize their structural a nd enzymatic differences. The epitopes of their extracellular domains, their molecular weights, and kinase activities were similar to rat ne u receptors expressed in fibroblasts. The receptors were partially pur ified using a phospho-agarose column and were analyzed to compare kine tic parameters using ATP as a substrate. The oncogenic form of the rec eptor showed a significant increase in V-max (56%) over the protooncog enic form. Structural analysis of these proteins using sucrose gradien ts showed the oncogenic receptors to have a 62.6% increase in aggregat ed receptors when compared to the proto-oncogenic receptors. These stu dies are the first to link enzymatic activation and the physical form of the receptor using isolated receptor species.