Fig. 4. The ionic current profile of different mutants on polypeptide (GGGGSGGGGSSGGGGSSGGSGGC): (a) S₅Q; (b) S₅F; (c) S₅D; (d) S₅E; (e)S₅DD; (f) S₅EE; (g) S₅QQ; (h) S₅SS, G₉E; (i) S₅H; (j) S₅KK; (k) S₅k; (l) phosphorylation of S₅; (m) S₅SS, phosphorylation of G₉S. (n) Comparison between I₁, which is measured based on the amplitude level of the initial steep current level rising, and I₂, which is the amplitude level of the main peak. The blue arrows point to the main peak; the red arrows point to the type of initial current rising (hump) induced by the negatively charged mutations or phosphorylation.