Polyelectrolyte field effects

Abstract

Sb'I~IARYPolyelectrolyte field effects are indicated by paxticularly large variations of thermodynamic and kinetic constants with ionic strength. Some fundamental principles of local electric field effects in the microenviz-onmen~; of polyelectrolyte struetura~ are discussed, aiming at a reliable analysis of shifts in equilibrium and rate constants of ionic reaction partners with ionic strength. It is shown that the analytical expressions, within certain limitations, are suitable to determine effective charges involved in polyionic field effects on ionic reactions in the immediate neighhorhood of a polyelectrolyte structure. An instructive example for such an observation is the neuro~nzyme acetylcholinesterase. The results of a relaxation--kinetic titration of this anionic enzyme (which hydrolyzes the cationic neuro-activator acetylcholine) with a cationic ligand suggest that the micro environment of the enzymeactive site consists of at least six anionic groups. A large effective, negative charge number is also reflected in the comparatively large association rate coefficients.These results suggest that an enzyme surface area considerably larger than the ligand binding site itself is effective in trapping a cationic ligand. This larger surface area may include peripheral anionic sites from which iigand would move to the active site by surface diffusion.

Influence of the Water Structure on the Acetylcholinesterase Efficiency

“…Neumann and Nolte (54) have proposed that ions can decrease the K m by binding to the active site of the AChE. To investigate separately the effect of the water structure disturbance and the putative effect of cation binding, we have carried out systematic kinetic experiments with increasing concentrations of ethanol.…”

Chemical electric field effects in biological macromolecules

“…Enokida et al, 1980). Practically, the ionic strength dependence of rate and equilibrium constants may be used in order to establish the mechanism of polyionic field effects Neumann and Nolte, 1981).…”

“…The relationship (59) may be used to estimate charge numbers of ionic binding sites on macromolecules in the framework of the Debye-Hiickel approximations (Nolte et al, 1980;Neumann and Nolte, 1981).…”