The self-association of zinc-free human insulin and insulin analogue B13-glutamine.

The self-association of Zn-free human insulin, Zn-free insulin analogue B13-glutamine, 2-Zn insulin and cobalt(III) human insulin in the millimolar concentration range has been investigated by measuring the osmotic pressure at pH 7.5 in 0.05 M NaCl, 25 degrees C. The pH dependence of association has been measured in the pH range 6.8-9. For all insulins, except Zn-free human insulin, the major association state has been found to be the hexamer. Maximal association of hexamer has been observed for Zn-free human insulin at high concentration (2-7 mM) and physiological pH. At concentrations less than 1 mM and pH greater than 7.0, dissociation to a lower state than the hexamer is found. The conclusion has been drawn that, in the absence of metal ions, human insulin and insulin analogue B13-glutamine associate to the hexamer in the physiological pH range at concentrations in the millimolar range.