Programmable chemical actuator control of soluble and membrane-bound enzymatic catalysis

Enzyme catalyzed reactions can be started, stopped, and throttled by regulating ion concentration in solution. The flow of charge through solution is related to the flow of electrons through an electric circuit using electrochemistry. However, current electrochemical methods to vary ionic concentration are largely limited to the electrode surface, making it impractical to exploit ionic concentration as a control variable in traditional enzyme assays. This chapter presents an electrochemical cell, termed a programmable chemical actuator (PCA), that uses selective electrochemical REDOX reactions to regulate the concentration of ions that control enzyme catalyzed reaction kinetics. The PCA is a polypyrrole polymerized and equilibrated to impart Mg²⁺, Mn²⁺, or OH^- ion selectivity to working electrodes. Duplex pulse amperometry demonstrated reversible control over the pH-dependent kinetics of alkaline phosphatase, a soluble homodimeric enzyme, during a spectrophotometric assay. PCAs were also used to extend electrochemical control to the membrane-bound enzyme complex rubber transferase by modulating Mg²⁺ and Mn²⁺ concentrations during a radiometric enzyme assay. PCAs demonstrated tunable control over rubber transferase activity and rubber molecular weight without dislodging either the elongating rubber molecule or irreversibly inhibiting the rubber transferase complex. This chapter presents methods to fabricate and operate PCAs to facilitate insights into the roles of ions in biochemical pathways and environmental responses in plants.