Effects of aplysia hemocyanin on the conductance of oxidized cholesterol black lipid membranes

The reaction of Octopus vulgaris hemocyanin with exogenous ligands: proposal of an allosteric model for the binding of cyanide and thiourea to the 11 S subunit

Octopus vulgaris hemocyanin in 11 S aggregation state binds oxygen following a noncooperative oxygen saturation curve with Hill coefficient n = 1. Under the same conditions the equilibrium and kinetics of the reaction with cyanide and other ligands are indicative of an anticooperative behavior displaying different characteristics for the different ligands. The data are consistent with an induced-fit type allosteric model which assumes for the 11 S subunit of O. vulgaris hemocyanin an annular structure made up by five identical domains each containing one binding site whose reactivity is near-neighbor regulated.

Antigen-antibody-complement reaction studies on micro bilayer lipid membranes

The ion permeability of lipid membranes formed on Millipore and Nuclepore filters has been found to exhibit stepwise reductions in electrical resistance in the presence of Forssman antigen, appropriate antiserum and complement. The results appear to support the "hydrophobic doughnut" or transmembrane channel hypothesis, which envisions several polypeptide chains anchoring from more than one terminal complement component to interact with one another within the lipid bilayer. Channel formation in these artificial membranes is believed to be due to the insertion of complement proteins. Concentrations and temperature studies were carried out to ascertain that the electrical responses were owing to the generation of stable channels by complement across the membrane. The diameter of these channels was estimated to be in the order of 100 A.

Electrical properties of ionic channels formed by Helix pomatia hemocyanin in planar lipid bilayers

Helix pomatia hemocyanin forms ion-conducting channels in planar lipid bilayer membranes when added at mg/ml concentration. These channels have several original features. They fluctuate between one conducting and some poorly conducting states and fluctuations can be grouped in bursts. Different channels can have widely different conductance amplitudes. Both channel conductance and burst lifetime are dependent on the applied voltage. Fluctuations within a burst show a complex kinetic behaviour which has been explained developing a multistate model. The model calls for one single open state and six different closed states. Transitions are allowed only between one of the closed states and the open one and obey first order kinetics. This model is able to fit all our experimental curves obtained in single channel experiments.

The dependence of the conductance of the hemocyanin channel on applied potential and ionic concentration with mono- and divalent cations

Incorporation of Megatura crenulata hemocyanin into phosphatidylcholine black lipid membranes results in the formation of ion channels. Channel properties depend on many factors, three of which are examined in this work: type and concentration of electrolyte and applied voltage. Eight cations at different concentrations have been used. Instantaneous conductance of the channel is a saturating function of both applied voltage and ionic strength of the bathing solution with monovalent cations, but only of ionic strength with divalent cations. Steady-state voltage-conductance relations are nonlinear for both signs but show slight saturation with ionic strength. Relaxation towards the steady state can be fitted by two exponentials with different time constants. All experimental data are fitted postulating the existence of a mechanism of voltage gating of the channel, and of discrete negative charge near its mouth. Specific and nonspecific binding of cations is required.