Trypsin sheds light on the singular case of seminal RNase, a dimer with two quaternary conformations

Dimeric seminal RNase presents the singular case of a dimer with access at equilibrium to two conformations: one in which the subunits exchange, or sw ap, their NH,terminal arms; the other with no exchange. Thus a continuous u nfolding/refolding of structural elements into two alternative conformation s takes place in the native protein at equilibrium. The phenomenon was inve stigated by kinetic and mass spectrometric: analyses of the effects of tryp sin on the native protein, on its isolated quaternary forms, as well as on a monomeric derivative of the protein and on homologous dimeric RNase A The kinetics of tryptic action on the protein forms and on the protein derivat ives, as well as the location of the tryptic cleavage sites, and their chro nological sequence, led to the identification of relevant interconversion i ntermediates, to the description of a model for the interconversion process , and to a hypothesis for the unique phenomenon of the dual quaternary conf ormation of seminal RNase.