Modification of arginines in bovine growth hormone

Treatment of bovine growth hormone with 1,2-cyclohexanedione - in borate buffer - selectively modified 11.8 out of the 13 arginines in the molecule. Kinetic analysis of the data showed a good fit to a pseudo first-order curve, with an apparent velocity constant k: 2 X 10(-2) min-1. The modification brought about a complete loss of bovine growth hormone capacity to compete with 125I-labelled hormone for rat liver binding sites. Circular dichroism studies indicated no apparent changes in protein conformation in the modified hormone. Full binding capacity was restored upon regeneration of arginines by hydroxylamine treatment. These results suggest that one or more arginines are involved in the binding of bovine growth hormone to its specific receptors. The non-reactive arginine was identified as arginine 181.