Figure 2.
Plots of log k′ versus N. k′ is the apparent first-order reaction rate constant for the reaction of the first cysteine in a homoheptameric cysteine mutant with a MePEG-OPSS reagent. N is the number of monomer units in a polymer. (A) MePEG-OPSS (4 mM) was applied from the trans side of the bilayer; (B) MePEG-OPSS (4 mM) was applied from the cis side. The reagents were: MePEG-OPSS-1k (N = 19, Mw/Mn = 1.02), MePEG-OPSS-1.8k (N = 39, Mw/Mn = 1.02), MePEG-OPSS-2.5k (N = 56, Mw/Mn = 1.03), and MePEG-OPSS-5k (N = 113, Mw/Mn = 1.02). The holding potential was −40 mV, as defined (25). The electrolyte in both chambers was 300 mM KCl/5 mM Tris⋅HCl, pH 8.5.