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W R Lieb

Publications and source records attributed to W R Lieb.

At least 73 records · Page 4Linked to original sources
PubMed1978

Where do general anaesthetics act?

General anaesthetics were found to have no effect on lipid bilayer structures when studied using X-ray and neutron diffraction. Combined gaseous and aqueous phase solubility data suggested that the primary site of action of general anaesthetics has both polar and nonpolar characteristics, and probably involves protein.

Anesthetics↗
PubMed1978

Diffusion within egg lecithin bilayers resembles that within soft polymers.

An analysis is presented of how the permeability coefficient/octanol:water partition coefficient ratio for 33 different chemical substances crossing egg lecithin bilayers depends on the molecular volume of the substances. From this analysis we conclude that bilayers made from egg lecithin behave as soft polymers in their discrimination between permeants of different sizes and shapes.

Diffusion↗
PubMed1976

Testing the simple carrier using irreversible inhibitors.

1. We analyse the kinetics of irreversible inhibition of the simple carrier. We consider how the rate of inactivation is influenced by the concentrations of permeant on the two sides of the membrane. 2. We consider various kinetic schemes for the simple carrier and show that these are all indistinguishable kinetically, using steady-state transport or inactivation data. We point out the advantages of using the simplest kinetic scheme and the possible pitfalls of using more complicated schemes, including the conventional carrier model. 3. We show that in the absence of information on the transport properties of the system, irreversible inhibition data are ambiguous. Taken together with transport data, however, inactivation data provide new tests for the applicability of the simple carrier. 4. The new tests show that for the simple carrier model to be applicable, the substrate dependencies of transport and of inactivation must be identical in comparable experimental situations. Further, the maximal rates of transport and of stimulation (or inhibition) of inactivation must obey a simple relationship, which we derive. We illustrate the use of these tests with published data on the glucose and choline transport systems of the human red blood cell.

Biological Transport↗
PubMed1973

A modle for active transport of sodium and potassium ions as mediated by a tetrameric enzyme.

A new model is proposed for the system that actively transports sodium and potassium ions across animal-cell membranes. The model is based on the physical and chemical properties of transport-associated adenosine triphosphatase (EC 3.6.1.3) and on the kinetics of ion movements mediated by the system. Transport is postulated to occur by internal transfer of cations across a protein tetramer embedded in the cell membrane. The protein tetramer can exist in either of two forms of identical energy; transport occurs as a result of the sequential "flipping" from one conformation to the other. The conformation change results in the interchanging of the affinities of cation-binding sites associated with different sub-units of the tetramer, with a concomitant splitting of adenosine triphosphate.

Adenosine Triphosphatases↗
PubMed1970

Quantitative predictions of a noncarrier model for glucose transport across the human red cell membrane.

There is an increasing amount of experimental data on transport across biological membranes which cannot be readily accommodated by classical mobile carrier models. We propose models for membrane transport based upon current concepts in molecular enzymology, in which the membrane component involved in transport is an oligomeric protein which undergoes substrate-induced conformational changes. A number of paradoxical observations on glucose transport in the human erythrocyte are explained if the protein involved is a tetramer possessing two classes of binding sites with different affinities for glucose. We develop in detail a particular model of this type, the internal transfer model, in which transport occurs by transfer of substrate from one subunit to another of the protein. The fit of the predictions of the internal transfer model with most of the experimental data is very good. Those data which cannot be fitted by the model cannot be accounted for by any presently available model. We extend our model qualitatively to include the sodium-activated cotransport systems for sugars and amino acids.

Amino Acids↗