Characterization of allosteric insulin hexamers by electrospray ionizationmass spectrometry

Electrospray mass spectrometry is used at pH 8.0 in combination with accura te mass measurements to confirm the multiplicity of insulin in stable nonco valent complexes with Zn(II) ions. Determination of the nature and number o f ligands involved in Zn(II) chelation is in agreement with crystal and sol ution structures. Counting the number of ligands participating in each cent er allows deduction of the geometric configuration of the ligand field and gives indirect information about the conformational state of the insulin mo nomers in solution.