Isaac Michaeli

Diffusion of adsorbed protein within the plane of adsorption

Abstract Bovine serum albumin, adsorbed onto half the surface of a glass coverslip, continues (under water) to creep along the glass surface until it covers the entire area, without having reentered the liquid phase.

Characterization of sodium and proton flows in sub-bacterial particles of Halobacterium halobium in terms of nonequilibrium thermodynamics

Abstract A thermodynamic characterization of the Na + -H + exchange system in Halobacterium halobium was carried out by evaluating the relevant phenomenological parameters derived from potential-jump measurements. The experiments were performed with sub-bacterial particles devoid of the purple membrane, in 1 M NaCl, 2 M KCl, and at pH 6.5–7.0. Jumps in either pH or pNa were brought about in the external medium, at zero electric potential difference across the membrane, and the resulting relaxation kinetics of protons and sodium flows were measured. It was found that the relaxation kinetics of the proton flow caused by a pH-jump follow a single exponential decay, and that the relaxation kinetics of both the proton and the sodium flows caused by a pNa-jump also follow single exponential decay patterns. In addition, it was found that the decay constants for the proton flow caused by a pH-jump and a pNa-jump have the same numerical value. The physical meaning of the decay constants has been elucidated in terms of the phenomenological coefficients (mobilities) and the buffering capacities of the system. The phenomenological coefficients for the Na + -H + flows were determined as differential quantities. The value obtained for the total proton permeability through the particle membrane via all available channels, L H = ( ∂J H + ∂Δ pH ) Δψ,Δ pNa , was in the range of 850–1150 nmol H + ·(mg protein) −1 ·h −1 ·(pH unit) −1 for four different preparations; for the total Na + permeability, L Na = ( ∂J Na + ∂Δ pNa ) Δψ,Δ pH , it was 1620–2500 nmol Na + ·(mg protein) −1 ·h −1 ·(pNa unit) −1 ; and for the proton ‘cross-permeability’, L HNa = ( ∂J H + ∂Δ pNa ) Δψ,Δ pH , it was 220–580 nmol H + ·(mg protein) −1 ·h −1 ·(pNa unit) −1 , for different preparations. From the above phenomenological parameters, the following quantities have been calculated: the degree of coupling ( q ), the maximal efficiency of Na + -H + exchange ( η max ), the flow and force efficacies (ϵ) of the above exchange, and the admissible range for the values of the molecular stoichiometry parameter ( r ). We found q ⩽ 0.4; η max ⩽ 5%; 0.36 ⩽ r ⩽ 2; ϵ J Na + ⩽ 1.3 · 10 5 μ mol · ( RT unit) −1 at J Na = 1 μmol Na + · ( mg protein ) −1 · h −1 ; and ϵ ΔpNa ⩽ 5 · 10 4 ΔpNa · (mg protein) · h · (RT unit) −1 at ΔpNa = 1 unit, for different preparations.

A thermodynamic analysis of the correlation between active Na+ transport and the rate of oxygen consumption in epithelia.

SummaryActive transport in epithelia is discussed in terms of the relationships between oxygen consumption and sodium flux as affected by each of the two corresponding thermodynamic forces. Analysis is presented of the use of nonequilibrium thermodynamics as a tool in elucidating coupling and stoichiometry, and in evaluating drug action in the system. The analysis leads to the quantitative characterization of active transport in “two-flow” systems in terms of two plots: oxygen consumption and sodium flow, each as a function of electrical potential difference, at constant affinity and constant concentrations. The relevant characteristic parameters are then shown to be represented by the slopes and intercepts of the two plots, the ratios of the slopes and of the intercepts, and by the difference—as well as the ratio—of the ratios. Distinction is made between experimental conditions in which the phenomenological coefficients remain constant and those in which these coefficients undergo appreciable changes. In terms of the above analysis, an examination is made of the effect of commonly used drugs. It is shown that while drugs may affect both the affinity and the phenomenological coefficients, they invariably affect the latter—at least in the cases hitherto reported.