The disulfide bond pairing of the pheromones E Euplotes raikovi

The disulfide pairings of the two Euplotes raikovi pheromones Er‐1 and Er‐2 have been determined by chemical and mass spectrometric analyses. Cystine‐linked peptides from thermolytic digestions of the native molecules were purified by reverse‐phase high performance liquid chromatography and identified in the known sequences to make the assignments. The same pairing, Cys(I)–Cys(IV), Cys(II)–Cys(VI), and Cys(III)–Cys(V), was found in both pheromones, suggesting that this pattern occurs commonly throughout this family of molecules. This arrangement of disulfides indicates that the three‐dimensional structure is defined by three loops, which can vary in size and charge distribution from one pheromone to another.