Thermal proteinoids as excitability-inducing materials

Murburn model of vision: Precepts and proof of concept

The classical paradigm of visual physiology comprises of the following features: (i) rod/cone cells located at the rear end of the retina serve as the primary transducers of incoming photo-information, (ii) cis-trans retinal (C₂₀ H₂₈ O) transformations on rhodopsin act as the transduction switch to generate a transmittable signal, (iii) signal amplification occurs via GDP-GTP exchange at transducin, and (iv) the amplified signal is relayed (as an action potential) as a flux-based ripple of Na-K ions along the axons of neurons. Fundamental physical principles, chemical kinetics, and awareness of architecture of eye/retina prompt a questioning of these classical assumptions. In lieu, based on experimental and in silico findings, a simple space-time resolved murburn model for the physiology of phototransduction in the retina is presented wherein molecular oxygen plays key roles. It is advocated that: (a) photo-induced oxygen to superoxide conversion serves as the key step in signal transduction in the visual cycle, (b) all photoactive cells of the retina serve as photoreceptors and rods/cones serve as the ultimate electron source in the retina (deriving oxygen and nutrients from retinal pigmented epithelium), (c) signal amplification is through superoxide mediated phosphorylation of GDP bound to inactive transducin, thereby activating a GDP-based cascade (a new mechanism for trimeric G-proteins), and (d) signal relay is primarily an electron movement along the neuron, from dendritic source to synaptic sink. In particular, we specify the roles for the various modules of transducin and GDP-based activation of phosphodiesterase-6 in the physiology of visual transduction.

Critical analysis of explanations for cellular homeostasis and electrophysiology from murburn perspective

Pursuits in modern cellular electrophysiology are fraught with disagreements at a fundamental level. While the membrane theory of homeostasis deems the cell membrane and proteins embedded therein as the chief players, the association-induction (or sorption/bulk-phase) hypothesis considers the aqueous phase of dissolved proteins (cytoplasm/protoplasm) as the key determinant of cellular composition and ionic fluxes. In the first school of thought, trans-membrane potential (TMP) and selective ion pumps/channels are deemed as key operative principles. In the latter theory, sorption-desorption dynamics and rearrangements of bulk phase determine the outcomes. In both these schools of thought, theorists believe that the macroscopic phase electroneutrality holds, TMP (whether in resting or in activated state) results solely due to ionic concentration differentials across the membrane, and the concerned proteins undergo major conformation changes to affect/effect the noted outcomes. The new entry into the field, murburn concept, builds starting from molecular considerations to macroscopic observations. It moots "effective charge separation" and intricate "molecule-ion-radical" electron transfer equilibriums as a rationale for ionic concentration differentials and TMP variation. After making an unbiased appraisal of the two classical schools of thought, the review makes a point-wise analysis of some hitherto unresolved observations/considerations and suggests the need to rethink the mechanistic perspectives.

The need for reconsideration of a mechanism of membrane potential generation using Ling's adsorption theory

Membrane theory attributes the mechanism of generation of membrane potential to transmembrane ion transport, and is typified by the Goldman-Hodgkin-Katz equation (GHK eq.). Despite broad acceptance of the GHK eq. in physiology, it seems unable to explain some characteristics of the membrane potential. The long-underrated Ling's adsorption theory (LA theory) is another mechanism for membrane potential generation. The LA theory attributes the generation mechanism of the membrane potential to an ion adsorption-desorption process. Although the LA theory has not been seriously considered up until today, there are no serious defects in it as a membrane potential generation mechanism. In this work, the authors explain problematic facets of membrane theory from the view of the GHK eq. We propose an alternative concept based on the LA theory that addresses problematic issues with membrane theory. Consequently, an ion adsorption-desorption process could be a genuine mechanism of membrane potential generation as predicted by the LA theory.

The murburn precepts for cellular ionic homeostasis and electrophysiology

Starting from the basic molecular structure and redox properties of its components, we build a macroscopic cellular electrophysiological model. We first present a murburn purview that could explain ion distribution in bulk-milieu/membrane-interface and support the origin of trans-membrane potential (TMP) in cells. In particular, the discussion focuses on how cells achieve disparity in the distribution of monovalent and divalent cations within (K⁺  > Na⁺  > Mg²⁺  > Ca²⁺ ) and outside (Na⁺  > K⁺  > Ca²⁺  > Mg²⁺ ). We explore how TMP could vary for resting/graded/action potentials generation and project a model for impulse conduction in neurons. Outcomes based on murburn bioenergetic equilibriums leading to solubilization of ion-pairs, membrane's permittivity, protein channels' fluxes, and proteins' innate ability to bind/adsorb ions selectively are projected as the integral rationale. We also provide experimental modalities to ratify the projections.

Towards proteinoid computers. Hypothesis paper

Proteinoids - thermal proteins - are produced by heating amino acids to their melting point and initiation of polymerisation to produce polymeric chains. Proteinoids swell in aqueous solution into hollow microspheres. The proteinoid microspheres produce endogenous burst of electrical potential spikes and change patterns of their electrical activity in response to illumination. The microspheres can interconnect by pores and tubes and form networks with a programmable growth. We speculate on how ensembles of the proteinoid microspheres can be developed into unconventional computing devices.

Synthesis of Copoly(amino acids) as Potential Biomaterials by Diphenyl Phosphoryl Azide

A convenient chemical synthesis of copoly(amino acids) as poten tial biomaterials is described. Direct copolycondensations of α-amino acids us ing diphenyl phosphoryl azide (DPPA) as condensation agent were carried out in the presence of triethylamine (TEA) as a base. The amino acids used were β-benzyl-L-aspartate (Asp.Bz), γ-benzyl-L-glutamate (Glu.Bz), L-phenylalanine (Phe), and O-benzyl-L-tyrosine (Tyr.OBz). Copoly(amino acids) with weight- average molecular weights up to 28,000 were obtained in reasonable yields. Bimodal molecular weight distribution was observed in all the cases. Both the overall yield of the product and the yield of high molecular weight fraction are influenced by [DPPA]/[Monomer] and [TEA]/[Monomer] ratios. No significant solvent effect was observed.

Amino Acid Oligomer Microspheres as Drug Delivery Systems. II. Oligomerization of NCAs Initiated with L-Tyrosine Methyl Ester

Oligomerizations of various amino acid N-carboxyanhydrides (NCAs) were prepared in the presence of L-tyrosine methyl ester (Tyr.Me). Tyr.Me was found to be an efficient initiator to form oligopeptides consisting of L-aspartic acid, L-glutamic acid, L-phenylalanine, and L-tyrosine with random arrangements of amino acids. In acidic solution, the oligopeptides formed microspheres which were capable of encapsulating macromolecular drugs such as insulin and heparin. These microspheres were considered to be potential oral drug delivery systems.

Amino Acid Oligomer Microspheres as Drug Delivery Systems. I. Synthesis of Oligo(Amino Acids) via NCAs and Their Microsphere Formation

Some thermally derived proteinoids are known to form hollow microspheres under specific conditions. In this study, oligomers consisting of L-aspartic acid, L-glutamic acid, L-phenylalanine, and L-tyrosine were prepared through the corresponding a-amino acid-N carboxyanhydrides (NCAs). The oligo(amino acids) synthesized by NCA method had better control on the composition as well as molecular weight. These oligo(amino acids) were found to spontaneously form microspheres under acidic conditions. It was also found that is possible to encapsulate a variety of drug entities within these unique self-assembling systems. The microspheres which form spontaneously at low pH's also dissolve in water at neutral pH and consequently have the potential to be used as oral drug delivery systems.

Ling's Adsorption Theory as a Mechanism of Membrane Potential Generation Observed in Both Living and Nonliving Systems

The potential between two electrolytic solutions separated by a membrane impermeable to ions was measured and the generation mechanism of potential measured was investigated. From the physiological point of view, a nonzero membrane potential or action potential cannot be observed across the impermeable membrane. However, a nonzero membrane potential including action potential-like potential was clearly observed. Those observations gave rise to a doubt concerning the validity of currently accepted generation mechanism of membrane potential and action potential of cell. As an alternative theory, we found that the long-forgotten Ling's adsorption theory was the most plausible theory. Ling's adsorption theory suggests that the membrane potential and action potential of a living cell is due to the adsorption of mobile ions onto the adsorption site of cell, and this theory is applicable even to nonliving (or non-biological) system as well as living system. Through this paper, the authors emphasize that it is necessary to reconsider the validity of current membrane theory and also would like to urge the readers to pay keen attention to the Ling's adsorption theory which has for long years been forgotten in the history of physiology.

Oscillatory phenomena in model membrane: electrical oscillation in lipid-impregnated membrane filter induced by alamethicin and controlled by bacteriorhodopsin

A lipid-impregnated membrane filter was able to show reproducibly of an electrical oscillation under constant current stimulation when alamethicin and protamine were present in the chamber whose salt concentration was higher than the other and the membrane was left for about 12 h. In addition, bacteriorhodopsin, which is a light-activated proton pump, was found to control the oscillation. The oscillatory phenomenon was considered to be driven by the alternating change in the ion-selectivity of the membrane between cation and anion. Impedance measurement indicated the existence of lipid rearrangement which might prepare an environment for both alamethicin and protamine to cause the oscillation.

Effects of thermal peptides on retention of footshock avoidance training in mice

Some hydrophobic polypeptides known as thermal proteins have been found to have neurotrophic effects. Thermal proteins were synthesized from aspartic acid, glutamic acid, proline, and tryptophan. Two hydrophobic and one nonhydrophobic polymers were injected intracerebroventricularly into brains of mice after partial training on footshock avoidance run in a T-maze. When retention was tested 1 week later, the hydrophobic polymers enhanced retention while the nonhydrophobic polymer did not. Thermal proteins exhibiting hydrophobicity and having neurotrophic effects may aid in altering synaptic connections by facilitating cell recognition.