Figure 4.

Effects of insulin on the formation of amyloid by IAPP in the presence of HS. (A) The results of thioflavin-T binding assays are displayed. The data are plotted as time normalized by the T₅₀ value of IAPP in the presence of HS, but in the absence of insulin: black, IAPP in the presence of HS; red, IAPP and insulin in a 20:1 ratio in the presence of HS; green, IAPP and insulin in a 5:1 ratio in the presence of HS; blue, IAPP and insulin in a 1:1 ratio in the presence of HS; pink, IAPP and insulin in a 1:5 ratio in the presence of HS; brown, a mixture of 80 μM insulin and 1.3 μM HS. (B) Expansion of the first five time units of panel A. The same color coding is used. (C) TEM image of IAPP in the presence of HS. (D) TEM image of a 1:5 mixture of IAPP and insulin in the presence of HS. Insulin is in 5-fold excess. (E) TEM image of the insulin/HS mixture. Aliquots were removed at the end of each reaction for TEM analysis. Scale bars represent 100 nm. The kinetic experiments were conducted in 20 mM Tris-HCl (pH 7.4) and 2% (v/v) HFIP without stirring at 25 °C. The IAPP concentration was 16 μM. The HS concentration was 1.3 μM.