From 1.2 x 106 male adult heads of the silkworm, Bombyx mori, 0.16 mg of bombyxin-IV was
isolated, which was a novel molecular species of bombyxin, previously called 4K-prothoracicotropic
hormone. Injection of 0.1 ng of bombyxin-IV into a dauer pupa of the Eri-silkworm,
Samia cynthia ricini, evoked adult development. Microsequencing, chemical modification,
enzymatic digestion, and fast atom bombardment mass spectrometry showed that
bombyxin-IV consisted of two heterogeneous peptides linked by disulfide bonds and had a
considerable sequence homology (62.5%) with bombyxin-II.