Binding of phenol to R-6 insulin hexamers

Small amounts of phenolic compounds are being used as preservatives in phar maceutical insulin preparations. It has been shown previously that these co mpounds bind to specific sites an the insulin hexamer and act as allosteric effectors, inducing a transformation of the T-6 hexamer to the R-6 hexamer , via a T3R3 intermediate. In this article, the crystal structures of eight different insulin derivatives, all in the phenol-containing R-6 form, are analyzed with respect to their phenol-binding sires. While six phenol molec ules are normally bound per insulin hexamer, one of the engineered insulins appears to contain only three phenols but yet exists in an R-6 conformatio n. This observation provides additional evidence for an inherent nonequival ence of the two trimers in the insulin he,hexamer, The unusual observation of a seventh phenol molecule bound to the hexamer of crystalline A21Gly-B31 ,B32Arg(2) insulin (HOE 901), a long-acting derivative currently undergoing phase III clinical trials, provides a partial explanation for its protract ed activity;. (C) 1999 John Wiley & Sons, Inc.