Phase behavior of ganglioside-lecithin mixtures. Relation to dispersion of gangliosides in membranes

Ganglioside GM1 and mixed brain gangliosides were mixed with 1-stearoyl-2-oleoyl lecithin (SOPC) and examined by differential scanning calorimetry as a function of ganglioside content and temperature. Low mole fractions of ganglioside GM1 and of mixed brain gangliosides are shown to be miscible with SOPC in the gel phase up to X = 0.3, with the possible exception of a small region of immiscibility for the mixed brain gangliosides system centered around X = 0.05. Above X = 0.3, the low-temperature phases demix into a (gel) phase of composition X = 0.3 and a (micellar) phase of composition X = 1.0. Above the endothermic phase transition temperature, no phase boundaries are discerned. It is pointed out that phase structures need to be determined in each domain delineated in the phase diagrams, and that cylindrical phases may exist at higher temperatures and intermediate compositions. The effects of addition of wheat germ agglutinin, which binds to ganglioside GM1, on a ganglioside GM1-SOPC mixture (X = 0.5), are described and interpreted in terms of partial demixing of ganglioside and lecithin. Behavior of the ganglioside-SOPC system is discussed with respect to the kinetics of cholera toxin action in lymphocytes, as well as to other physiological roles of gangliosides in membranes

Determination of the distribution of catalyst activity across a permeable membrane containing an immobilized enzyme. Indeterminacy of a functional approach to a structural problem

Porous membranes were fabricated from collodion and impregnated with papain, inhomogeneously through the thickness of the membrane. These membranes were placed between reservoirs containing N-alpha-benzoyl arginineamide, a substrate for the enzyme papain. The progress of the reaction was monitored by sampling the reservoirs on each side for ammonia, a reaction product. From these data the diffusion coefficient, enzyme activity, and distribution of enzyme activity of the membrane were estimated. The limitations of this approach are discussed in the context of the analysis of biological transport systems

Complete analysis of the cytochrome components of beef heart mitochondria in terms of spectra and redox properties. Cytochromes aa3

Using newer techniques of data collection that accumulate entire spectra at a series of discrete voltages and newer techniques of analysis that utilize the additional data, we have re-examined the redox behavior and corresponding difference spectra of redox centers responsible for the alpha absorbance features of cytochromes aa3 in beef heart mitochondria. Our analysis reveals three Nernstian components with Em values of 200, 260, and 340 mV with n values of 2, 2, and 1, respectively. The maximum alpha absorbance in the difference spectra for each of these species is located at 602, 605, and 607 nm respectively. Titrations in the presence of carbon monoxide led to the identification of the lowest voltage species as cytochrome a3. The Em of the carbon monoxide-liganded species was not raised. This is contrary to the result expected when a ligand has a much stronger affinity for the reduced form of a redox couple than the oxidized form. It is, however, consistent with a proton-pumping model of cytochrome oxidase in which the binding of ligand results in the dissociation of protons