A few distinct 'molecular sandwiches' are basis for structural and functional similarities of subspecies of interferon alpha and of families of growth-promoting hormones.

'Molecular sandwiches' composed of two aromatic amino acids separated by a hydrophilic one were found on eleven subspecies of human interferon alpha, on murine interferon alpha 2, and human interferon beta 1. In addition, another type of the sandwiches was found on several species of interferon. This confirms and extends the observations concerning the similarities between some interferons and several classical hormones. Furthermore, we are presenting evidence that a distinct type of the 'molecular sandwiches': Tyr-Cys...Cys and/or Cys...Cys-Cys...Cys, that participate in formation of disulfide bonds, is a characteristic marker of most, if not all of the growth-promoting hormones including growth factors. The 'sandwiches' appear to be important for receptor binding.