Hydrogen/deuterium exchange of monomers and dimers of leucine enkephalin

Leucine enkephalin has been studied using the combination of electrospray ionization (ESI) with a fast flow technique, ESI of leucine enkephalin produces an isotopic multiplet of peaks beginning at m/z 556. Hydrogen/deuterium exchange of this multiplet with ND3 has revealed the contribution of two ion populations to this multiplet: The singly protonated monomer and the doubly protonated. dimer. These populations were separated through their different kinetic behavior. Whereas the dimers undergo slow exchange the monomers undergo pronounced complexation with ND3 and display a fast exchange of four labile hydrogens. The results indicate a more compact globular structure for the diprotonated dimer. (C) 2002 Elsevier Science B.V.