A new proposal regarding the transport mechanism of mercury in biological membranes

The interactions of mercury (Hg²⁺) with biological membranes have been investigated. The experimental results indicate that Hg²⁺ induces a rapid alkalinization in energized Lysosomes from rat liver. The interpretation of the process is that the mercury enters the Lysosomes as a Hg(OH)₂ electroneutral compound, thus inducing alkalinization in the matrix.     

The mutual binding exclusion mechanism in active transport across biological membranes

The coupling mechanism of sarcoplasmic reticulum ATPase is based on the reciprocal influence of calcium binding and phosphorylation domains. Cooperative calcium binding activates the enzyme, permitting utilization of ATP by transfer of its terminal phosphate to the enzyme. Occupancy of the phosphorylation domain then produces internalization and dissociation of the bound calcium. Hydrolytic cleavage of P_i completes the catalytic and transport cycle. Conversely, the phosphorylated enzyme intermediate can be formed with P_i in the absence of Ca²⁺. This intermediate is then destabilized by calcium binding, permitting formation of ATP by phosphoryl transfer to ADP.     

Chemiosmotic mechanism of transport of biological macromolecules through bacterial membranes]

A general mechanism of the nucleic acids transport through bacterial membranes during genetic transformation, transfection, viral infection and bacterial conjugation, has been developed. The uptake of nucleic acid occurs due to the symport with H+ ions down to an electrochemical potential gradient ("minus" inside) generated by respiration or ATP hydrolysis within recipient cells. The nucleic acid anions of non--lethal viruses are extruded from the negatively charged host cell cytoplasm by electrostatic repulsion. The difference of electrochemical potentials between the conjugating cells cytoplasms is considered as a driving force for the transport of DNA from the donor to the recipient cell.     

On a possible mechanism for biological periodicity

It is shown that osmotic coupling between solutes, leads, under certain conditions, to differential equations of penetration which have periodic have very similar colligative properties, but that their concentrations in the external medium be quite different. It is noted that isotopes may satisfy these conditions exactly, and that they have been observed experimentally to penetrate as predicted. The differential equations bear a resemblance to the interactive equations of Volterra and Lotka.     

A mechanism for active transport of coenzyme-like substances with possible reference to auxin transport in plants

A geometrically constrained enzyme system is presented which is capable of driving a substance, which acts as a coenzyme to one of the enzymes of the system, against a concentration gradient. The energy for the process would be derived from the breakdown of the substrate for the enzyme-coenzyme system. If auxin-like substances act in the manner of a coenzyme in plants, then the mechanism presented might serve as a model to explain the polar transport of such substances in plants.     

Association dynamics and lateral transport in biological membranes

A theoretical analysis is presented for the interrelated effects of lateral diffusion and a simple form of molecular association (A + B ? C) in biological membranes. Expressions are derived for the characteristic functions measured in fluorescence redistribution after photobleaching experiments, corresponding to both the Fourier transform analysis of concentration in a plane and the normal mode analysis for a spherical surface. The results are related to the reputed binding of integral membrane proteins to submembranous cytoskeletal elements.     

A novel mechanism of interaction between alpha-synuclein and biological membranes

Conformational abnormalities and aggregation of alpha-synuclein (alpha-syn) have been linked to the pathogenesis of Parkinson's (PD) and related diseases. It has been shown that alpha-syn can stably bind artificial phospholipid vesicles through alpha-helix formation in its N-terminal repeat region. However, little is known about the membrane interaction in cells. In the current study, we determined the membrane-binding properties of alpha-syn to biological membranes by using bi-functional chemical crosslinkers, which allow the detection of transient, but specific, interactions. By utilizing various point mutations and deletions within alpha-syn, we demonstrated that the membrane interaction of alpha-syn in cells is also mediated by alpha-helix formation in the N-terminal repeat region. Moreover, the PD-linked A30P mutation causes reduced membrane binding, which is concordant with the artificial membrane studies. However, contrary to the interaction with artificial membranes, the interaction with biological membranes is rapidly reversible and is not driven by electrostatic attraction. Furthermore, the interaction of alpha-syn with cellular membranes occurs only in the presence of non-protein and non-lipid cytosolic components, which distinguishes it from the spontaneity of the interaction with artificial membranes. More interestingly, addition of the cytosolic preparation to artificial membranes resulted in the transient, charge-independent binding of alpha-syn similar to the interaction with biological membranes. These results suggest that in cells, alpha-syn is engaged in a fundamentally different mode of membrane interaction than the charge-dependent artificial membrane binding, and the mode of interaction is determined by the intrinsic properties of alpha-syn itself and by the cytoplasmic context.     

A possible model for receptors in excitable membranes

A model is proposed for receptors in excitable membranes based on the following assumptions. The receptor site and the process it excites in the membrane are located close to each other. The change of the electrostatic potential in the neighbourhood of the receptor site on the adsorption of a molecule (or ion) influences a potential dependent process in the membrane, such as ion permeability, rate of enzymatic reactions, ion binding etc. A comment is also made about the connection between measured physiological activity of a molecule and its ?real” physical activity.     

Charge trapping by solitions—A possible transport mechanism in macromolecular systems

Macromolecules and their aggregates possess polar modes which, when excited, cause deformations, which provoke in turn elastic restoring forces. Even the simplest of such models (involving polarization and elastic modes along a chain) admit localized excitations (solitons) endowed with a characteristic degree of stability; and these provide a mechanism for charge trapping which may be of importance in the understanding of the elusively high efficiency of charge transfer over macroscopic distances evidently involved in various biomolecular processes.     

Bisoliton mechanism of electron transport in biological systems

A nonlinear mechanism describing the transport of paired electrons in protein molecules is suggested. It is shown that electron-phonon interaction leads to the pairing of two electrons with local chain deformation in a state called a bisoliton. The parameters of the bisoliton and the stability conditions with respect to its decay into two-soliton state are estimated.I dedicate this paper to the memory of my teacher Professor A.S. Davydov, who attracted me to nonlinear science and was my colleague.     

Possible mechanism of ATP formation in energy-transforming biological membranes

An "elementary act" of ATP formation from ADP and Pi in energy-transducing organels (mitochondria, chloroplasts and chromatophores) can be realized without closed membrane vesicles, pieces of membranes and F0-component of H+ATPase. The "elementary act" is initiated by a rather fast deprotonation of several acid groups of the coupling factor F1 (or CF1), this process leads to structurally non-equilibrium state of the enzyme due to the appearance of "additional" negative charges in unchanged protein globula. The endergonic step of ATP synthesis, i. e. release of tightly-bound ATP into the aqueous medium, occurs during conformational relaxation of the non-equilibrium state of H+ATPase. Closed membrane vesicles are necessary for a cyclic return of the enzyme to the initial state with protonized functional groups, this provides multiple synthesis of ATP under the steady state and quasi-stationary conditions. The energetical aspects and details of possible schemes of ATP synthesis initiated by artificial electrochemical gradient of protons, as well as ATP formation during oxidative and photophosphorylation are discussed here.     

27Al-NMR studies of aluminum transport across yeast cell membranes

Aluminum (Al) transport across yeast cells was studied using Dy(NO₃)₃ as a shift reagent by ²⁷Al-NMR spectroscopy. The results showed that (a) Al enters the yeast cells at 15 min and over a period of time, within 4 h, an equilibrium sets in between outside and inside Al; (b) citrate does not favor Al going into the yeast cells at pH 5.0; and (c) EDTA brings out all the Al that has entered the yeast cells. (Mol Cell Biochem 175: 59–63, 1997)