Figure 9.Model of the different conformational states of metal coordinated (hexameric), and monomeric, insulin. The thick line represents the B-chain, the thinner line represents the A-chain of an insulin monomer, and the amino terminus of each chain is indicated by a ball. The arrow in each illustration gives the location of PheB25, cyclohexanol is represented as a striped hexagon, and hydrogen bonds are represented as dotted lines. It can be seen that the major difference between the metal coordinated TM and RM-state is the reorganization of hydrogen bonding at the B-chain NH2-terminus, allowing two additional turns of helix, and alteration of PheB25 in the RM-state. The TI and RI-state, which are independent of metal ion coordination, differ in a similar manner, however, the b -sheet region of the B-chain COOH-terminus in the RI-state is not as well defined as in the RM-state.