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Biomedical subjects

D A Haydon

Publications and source records attributed to D A Haydon.

At least 55 records · Page 3Linked to original sources
PubMed1979

Fusion of photoreceptor membrane vesicles.

The n-alkyl bromides with 6 to 10 carbons induce formation of vesicles of 5 to 100 micrometer diameter from the small vesicles (0.1 micrometer average diameter) produced by disruption of the discs from frog rod photoreceptors. The n-alkanes, n-alkyl iodides and n-alkyl chlorides are relatively ineffective. The formation of large vesicles is independent of calcium concentration and is distinguished from fusion processes previously reported by the large number of vesicles involved. The results reported here together with others suggest the occurrence of multiple fusion (and/or rupture-resealing) events between vesicles, induced by the n-alkyl bromides.

Animals↗
PubMed1978

The blockage of the electrical conductance in a pore-containing membrane by the n-alkanes.

1. In monooelein bilayers made highly conducting by the addition of a fixed amount of o-pyromellitylgramicidin, the membrane conductance has been shown to be strongly dependent on the chain length of the n-alkane with which the membrane is in equilibrium. Thus for n-hexadecane, the conductance is larger by approx. 10(4) times than it is for n-octane. This result is independent of whether the polypeptide is introduced via the aqueous or lipid phases. 2. The observed conductance variations have been accounted for in terms of a mechanism (outlined in earlier publications) which is based on the thickness and tension changes produced in bilayers by the adsorption of n-alkanes. Essentially quantitative agreement between theory and experiment is found.

Alkanes↗
PubMed1978

The kinetics of ion movements in the gramicidin channel.

The main features of the ion permeability of gramicidin channels are summarized. The significance of maximums in the single channel conductance-concentration curves, of concentration-dependent permeability ratios, and or current-voltage curves with concentration-dependent form, as well as of other features, is discussed in terms of the mechanism of the ion transfer processes. The observations are then shown to be accounted for by rate theory expressions derived for a model pore consisting of two sites in series and in which ions are not permitted to pass each other. The status of other models is briefly reviewed.

Anions↗
PubMed1976

Kinetics and stability of alamethicin conducting channels in lipid bilayers.

It is already well-established that conduction in lipid bilayers containing alamethicin arises from the presence of complexes in which there are several molecules of the polypeptide. It is with the nature of these complexes that this paper is primarily concerned. While it is clear that increasing alamethicin concentration and increasing potential across the membrane favour their formation, the nature of the reactions involved has not yet been elucidated. Attempts have therefore been made to clarify the sequence of events leading to the establishment of a complex in its conducting state. It has been concluded that the most likely mechanism involves, initially, a non-field-dependent aggregation of the alamethicin, in the plane of the membrane, into non-conducting oligomers. These then appear to undergo movement normal to the membrane (which is field dependent) to form the conducting species. Temperature studies have shown that the various conducting states of the oligomer have effectively equal enthalpies, and that the activation energies for transitions between these states are all approx. 1.2kcal/mol. The corresponding rate constants are very sensitive to the lipid composition of the membrane and a variety of different systems has been examined in order to clarify the origins of this effect. The only conclusion from this part of the work is that lipid fluidity might be involved.

Alamethicin↗
PubMed1976

The adsorption of lysine vasopressin at ionized interfaces.

It has been shown by surface potential measurements that lysine vasopressin and oxytocin may be bound by ionic surfaces to very varied extents. To dodecyl sulphate and phosphatidylserine monolayers the binding is very strong and is comparable to that for biological receptors such as those in toad bladder. For dioleyl phosphate and the carboxyl group of the polypeptide alamethicin, the binding is rather weaker while, for the zwitterionic lipids phosphatidylcholine and phosphatidylethanolamine, and for the erythrocyte surface, which contains two varieties of carboxylic acid group, no interaction seems to take place. In no system does the lysyl amino group of the vasopressin appear necessary for adsorption and, in the dodecyl sulphate monolayers, the interaction is strong even when the ionization of the terminal alpha-amino group is suppressed.

Animals↗
PubMed1975

Potential-dependent conductances in lipid membranes containing alamethicin.

This article is concerned primarily with the mechanism of the potential-dependent conductance induced in artificial lipid membranes by the cyclic polypeptide andibiotic alamethicin. It has already been shown from studies of the fluctuations that can be detected in very small membrane currents that alamethicin forms transient pores of some 0.6 nm in diameter and that, for small inorganic ions, these are poorly selective. The origin of these pores, their spatial distribution and interaction are discussed. It is demonstrated that the sensitivity of the membrane conductance to the applied potential arises only to a slight extent from the current-voltage relations for the individual pores, and that the main effect stems from the influence of the potential on the frequency of opening of the pores. From the properties of lipid membranes containing alamethicin in a wide variety of electrolytes, and from other evidence, it is concluded that the polypeptide reacts to the electric field more probably because it has dipole moment than because it binds ions. It is proposed that the conducting complex is capable of functioning in either of two orientations, and that it is these two possibilities that give rise to certain differences in the single channel characteristics for the two directions of the field.

Alamethicin↗