Theoretical Studies of a Glucagon Fragment: Ser8-Asp9-Tyr10 Abstract: The mutation Asp9Glu greatly reduces the signal trandsuction capability of glucagon while not affecting its binding ability to its receptor. Ab initi calculations were perfomed on the Ser-Asp-Tyr and Ser-Glu-Tyr to determine their lowest energy conformation. The difference between the two tripeptide's optimal conformations was analyzed for possible explanation of the difference in their behaviour.