Figure 3 shows the square wave voltammograms of 5.1��10-5 M hIAPP incubated at 37 ��C for different times. Obviously, the oxidation peak declines as the incubation period increases. This is reasonable, since the C-terminal tyrosine residue is accessible to the electrode surface and easily oxidized if it is in the soluble form. When hIAPP converts to its insoluble ��-sheet fibrillar aggregation state, the tyrosine residues become somewhat inaccessible to electrode surface, which thus causes the observed decline of the oxidation peak.Figure 4(A) shows the relationship between the oxidation peak current and the incubation time (R.S.D.: 0.73% ~ 2.02% for three measurements). During the incubation period the peak current is nearly unchanged from 0 to 1 h.

This result may be due to a multistep nucleation-aggregation and concentration-dependent process that proceeds via a conformational transition of mainly random coil hIAPP into ��-sheet-containing amyloid aggregates. At the beginning of the aggregation process, a nucleation period during which soluble oligo- and multimeric hIAPP are formed is necessary [10, 16, 33, 34]. This period may have little influence on the oxidability of the tyrosine residue in C-terminal of hIAPP. However, as the nucleating period is finished and multimeric hIAPP seeds are formed, a conformational transition process starts, accompanied by a rapid decrease of the free tyrosine residues. As a result, as shown in Figure 4(A), the peak current declined rapidly during the incubation period from 1 to 3 h.

After the three hour incubation period, the peak current of hIAPP reaches a minimum and can be hardly changed with a further prolonged incubation period, which suggests that hIAPP has completed changed its conformation from a soluble monomer to amyloid aggregates within the three Dacomitinib hours.Figure 4.(A) Relationship between the oxidation peak current in the square wave voltammograms of hIAPP and the incubating period. (B) Relationship between the fluorescent intensity of thioflavin-T treated hIAPP solution and the incubating period. Others same as …We have further compared the electrochemical analysis with a referenced thioflavin-T based fluorescent assay. Thioflavin-T and its derivatives can bind to amyloid fibrils in a specific, regular fashion, thus the increase in thioflavin-T fluorescence emission has been broadly used as a specific and quantitative assay for fibril formation. Figure 4(B) shows the relationship Carfilzomib between fluorescent intensity of thioflavin-T treated hIAPP solution and the incubation period.