Specificity of Hybrid Proteins. ∗

Abstract

As a result of crossing female domestic Ring doves with males of an Asiatic species, Irwin 1 reports the emergent evolution of a new protein specificity in hybrid doves, no trace of which is demonstrable in the erythrocytes of either parent.

To throw light on the probable immunochemical mechanism involved in this apparent non-conformity with Mendelian laws, we have tried to produce analogous test-tube hybridizations between proteins of 2 widely different animal species.

Serum proteins of the horse and domestic swine were selected for this purpose. To bring about rapid hybridization between these proteins, horse serum and swine serum were mixed in equal proportions, the resulting mixture diluted with 3 volumes of distilled water and then heated to 120°C. for 30 minutes. After cooling, the osmotic pressure was restored to normal by the addition of NaCl. As controls, unmixed horse serum and swine serum were similarly diluted, heated and restored to normal osmotic pressure.

Rabbits were immunized against the artificial horse-swine hybrid serum. A typical set of serological tests with the resulting anti-hybrid precipitin is recorded in Table I.

From the table it is seen that the artificial horse-swine hybrid serum contains one or more specific factors not present in horse serum or swine serum.

If an analogous fusion of paternal and maternal protein specificities takes place during sexual reproduction, the apparent emergent evolution of one or more new protein characters in certain hybrids would be in accord with Mendelian laws.

The above data are consistent with the current theory that the specific antigenicity of a given biological product is not determined solely by its specific haptene content, but is largely dependent on the topographical distribution of these haptenes on or within colloidal molecules.