Portal de Periódicos da CAPES

Chapter 14 Reaction-Kinetic Analysis of Current-Voltage Relationships for Electrogenic Pumps in Neurospora and Acetabularia

1982; Elsevier BV; Linguagem: Inglês

10.1016/s0070-2161(08)60704-2

1875-6492

D. Gradmann, Ulf‐Peter Hansen, Clifford L. Sla Yman,

Plant and Biological Electrophysiology Studies

Enzyme-mediated ion transport processes constitute a special class of reactions, which are subject to two separate sets of constraints: those of enzyme kinetics, and those of electric circuit theory. Since the electrical properties of many biological membranes–and, under special conditions, of specific ion transport systems–are relatively easy to measure, the question naturally arises as to how the electrical behavior of a transport system can illuminate underlying reaction mechanisms. This chapter explores the functional dependence of current flow through electrogenic ion pumps upon the magnitude of the imposed membrane potential and then to relate this so called current-voltage relationship (I–V relationship) to the predicted behavior of certain kinds of kinetic models for transport. Class-I electrogenic models are discussed: those having a single limb in which charges are transferred across the membrane. Since the extraction of kinetic information from I–V relationships depends strongly on observable nonlinearities. The presentation of experimental results is restricted to two electrogenic ion pumps for which nonlinear I–V relationships have been documented: ATP-driven extrusion of protons across the plasmalemma of the ascomycete fungus, neurospora crassa and the electrogenic uptake of chloride by the unicellular green marine alga, acetabularia mediterranea.