Characterization of allosteric insulin hexamers by electrospray ionization mass spectrometry

Electrospray mass spectrometry is used at pH 8.0 in combination with accurate mass measurements to confirm the multiplicity of insulin in stable noncovalent complexes with Zn(II) ions. Determination of the nature and number of ligands involved in Zn(II) chelation is in agreement with crystal and solution structures. Counting the number of ligands participating in each center allows deduction of the geometric configuration of the ligand field and gives indirect information about the conformational state of the insulin monomers in solution.