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Various enzymatic derivatives of the murine myeloma protein IgAMOPC-315were 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 ε-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 IgAMOPC-315but also introduced disparity with respect to binding kinetics, i.e., Kvalues of 2.31 × 106, 6.62 × 106, and 2.06 × 107M-1were determined for IgAMOPC-315, Fab′MOPC-315, and FvMOPC-315, respectively. We speculate that the results can be explained by possible modulating effects on haptenbinding contributed by novel conformations introduced through proteolysis.

Single interstitial stem cells of male polyps of Hydra magnipapillatagive rise to clones that differentiate either male or female gametes. To test the sexual stability of these clones, stem cells were recloned. The results indicate that stem cells from female clones are stable in their sexual differentiation capacity; male stem cells, by comparison, switch sexual phenotype at the rate of 10-2per cell per generation. As a result, female polyps contain only female stem cells; male polyps contain a mixture of male and female stem cells. A model is presented in which the sexual phenotype of Hydrapolyps is controlled by (i) the switching rate of male and female stem cells and (ii) the repression of female differentiation by male stem cells.