The reaction between proteins and reducing sugars in the ‘dry’ state. Relative reactivity of the α- and ∈-amino groups of insulin

Abstract

The reaction at 37[degree] between insulin and glucose freeze-dried together from soln. at pH 7 was investigated. The rate of reaction increased activity of water to a max. at a water content in equilibrium with a relative humidity of approx. 70%, a nd thereafter to decrease again with further increase in water content. The reactivities towards glucose of the alpha- amino groups attached to the terminal phenylalanyl and glycyl residues, and of the epsilon-amino groups attached to the lysyl residues of insulin were detd. by the fluoro-dinitrobenzene method. After 4 days at 65% relative humidity, 70% of the phenylalanyl amino groups, 37% of the glycyl amino groups and only 21% of the lysyl amino groups had reacted. After 16 days the corresponding figures were 80, 66 and 55%.