Water at Biological Phase Boundaries: Its Role in Interfacial Activation of Enzymes and Metabolic Pathways

Abstract

Many life-sustaining activities in living cells occur at the membrane-water interface. The pertinent questions that we need to ask are, what are the evolutionary reasons in biology for choosing the membrane-water interface as the site for performing and/or controlling crucial biological reactions, and what is the key physical principle that is very singular to the membrane-water interface that biology exploits for regulating metabolic processes in cells? In this chapter, a hypothesis is developed, which espouses that cells control activities of membrane-bound enzymes through manipulation of the thermodynamic activity of water in the lipid-water interfacial region. The hypothesis is based on the fact that the surface pressure of a lipid monolayer is a direct measure of the thermodynamic activity of water at the lipid-water interface. Accordingly, the surface pressure-dependent activation or inactivation of interfacial enzymes is directly related to changes in the thermodynamic activity of interfacial water. Extension of this argument suggests that cells may manipulate conformations (and activities) of membrane-bound enzymes by manipulating the (re)activity of interfacial water at various locations in the membrane by localized compression or expansion of the interface. In this respect, cells may use the membrane-bound hormone receptors, lipid phase transition, and local variations in membrane lipid composition as effectors of local compression and/or expansion of membrane, and thereby local water activity. Several experimental data in the literature will be reexamined in the light of this hypothesis.

Mechanisms and applications of the anti-inflammatory effects of photobiomodulation

“…At present the proposed mechanism involves selective absorption of IR photons by structured water layers (also known as interfacial water) [26] or water clusters [27], at power levels that are insufficient to cause any detectable bulk-heating of the tissue. A small increase in vibrational energy by a water cluster formed in or on a sensitive protein such as a heat-gated ion channel, could be sufficient to perturb the tertiary protein structure thus opening the channel and allowing modulation of intracellular calcium levels [28]. Pollack has shown that interfacial water can undergo charge separation when it absorbs visible or NIR light [29].…”

The impact of lipases on the rheological behavior of colloidal silica nanoparticle stabilized Pickering emulsions for biocatalytical applications

“…To cover the high demand of synthesis involving hydrophobic substrates and/or products, biocatalysis in unconventional media (i.e., organic solvents) is a powerful technique leading to high yields [1][2][3]. However, biocatalysts require a minimum water activity in the media to achieve an adequate catalytic activity [4][5][6]. To provide this, two-phase systems in which the biocatalyst is located in the aqueous phase, guaranteeing its activity, and the hydrophobic reactants predominate in the organic phase are promising alternatives.…”

Effect of Phospholipid Headgroup Charge on the Structure and Dynamics of Water at the Membrane Interface: A Terahertz Spectroscopic Study

“…The membrane interface (see Figure a) ensures a dynamic segregation of the bulk (outer) aqueous phase from the more isotropic, hydrophobic membrane core and exhibits distinct chemical, motional, and dielectric signatures . This region, owing to its unique physicochemical properties, plays a crucial role in modulating biochemical processes such as substrate recognition and function of membrane-active enzymes. − At a molecular level, the membrane interface imposes a dynamic spatiotemporal confinement on water molecules due to reduced probability of energetically favorable hydrogen bonding induced by geometrical constraints . As a result, the membrane interface displays slow rates of solvent relaxation and is involved in intermolecular charge interactions and hydrogen bonding mediated by polar phospholipid headgroups. , …”