Multiphasic profiles for the biologically important ion activities of NaCl and KCl

TL;DR

This paper demonstrates that the multiphasic profiles observed in biological ion activities are also inherent in the fundamental physical properties of ions, revealing a universal pattern across biological and inorganic systems.

Contribution

It shows that multiphasic ion activity profiles are intrinsic to the ions themselves, not just biological processes, through reanalysis of extensive inorganic solution data.

Findings

Multiphasic profiles are present in inorganic ion activities.

Ion activities can be accurately modeled by multiphasic profiles.

The multiphasic nature is inherent to the physical properties of ions.

Abstract

When plotted in linear transformations of the Michaelis-Menten equation, ion uptake in plants has been shown to be multiphasic, i.e. to be represented by a series of straight lines separated by discontinuous transitions (Nissen 1971, 1974, 1991, 1996). Reanalysis of data for other transport, binding and enzyme systems has also given such kinetics (Nissen and Mart\'in-Nieto 1998). Recently, such profiles have been found for a variety of biological as well as non-biological processes and phenomena, including activation of ion channels, binding, pH, folding/unfolding, effects of various interactions and chain length (Nissen 2015a,b, Nissen 2016a-d). These biological and nonbiological processes have little in common beyond the ions involved. Here I show that the multiphasic property seen in so many systems is present in the fundamental physical properties of the ion themselves. The characteristics of multiphasic profiles have now also been found in profiles for activities of ions in simple inorganic solutions, indicating that they are somehow causing the multiphasic profiles in more complex systems. A set of extensive and precise data (Lee et al. 2002) for the activities of the biologically very important ions Na+, K+ and Cl- (in NaCl and KCl) at four different temperatures (15, 25, 35 and 45oC) will be reanalyzed in the present paper. The activities of NaBr and KBr will be plotted in a forthcoming paper. Extensive data for these and other ion activities Wilczek-Vera et al. (2004) can also be precisely represented by multiphasic profiles (in preparation).