A functional examination of hapten-binding derivatives from a murine myeloma protein with immunoglobulin features

Abstract

Various enzymatic derivatives of the murine myeloma protein IgA(MOPC-315) were subjected to hapten-binding quantitation and circular dichroic analysis in an attempt to ascertain the structural localization and functional definition of the immunoglobulin active site. The extrinsic Cotton effects observed with near saturation of the active site of the derivatives using epsilon-Dnp-L-lysine were qualitatively and quantitatively identical when normalized with respect to their macromolecular content of Dnp-binding sites; ellipticity maxima of 378 and 438 nm and an ellipticity minimum of 325 nm were recorded. Fluorescence quenching data confirmed the molecular nature of the derivation products of IgA(MOPC-315) but also introduced disparity with respect to binding kinetics, i.e., K values of 2.31 x 10(6), 6.62 x 10(6), and 2.06 x 10(7) M(-1) were determined for IgA(MOPC-315), Fab'(MOPC-315), and Fv(MOPC-315), respectively. We speculate that the results can be explained by possible modulating effects on haptenbinding contributed by novel conformations introduced through proteolysis.