Inner mitochondrial membranes bound to concanavalin A-sepharose display succinate dehydrogenase, ATPase, and cytochrome oxidase activity

Adsorptive immobilization of erythrocyte membrane

Immobilization of human erythrocyte membrane was carried out by adsorption on Fractosil, a porous form of silica. Acetylcholinesterase (AChE) was chosen as a representative membrane enzyme in this study. Dependency of adsorption on membrane concentration was determined. Positive cooperative interactions that occurred in the process of immobilization increased stability. Presence of hydrophobic ligands on derivatized Fractosil was found to enhance stability of immobilized preparations making them more effective for use in continuous catalytic transformations. It is suggested that adsorptive immobilization of membrane structures such as the human erythrocyte membrane fragments on Fractosil and other inexpensive supports may provide a convenient procedure for utilization of their catalytic potential. Such preparations may be used in diagnostic kits or for construction of biosensors.

Chromatographic methods to study protein-protein interactions

Proteins and enzymes are now generally thought to be organized within the cell to form clusters in a dynamic and versatile way, and heterologous protein-protein interactions are believed to be involved in virtually all cellular events. Therefore we need appropriate tools to detect and study such interactions. Chromatographic techniques prove to be well suited for this kind of investigation. Real complexes formed between proteins can be studied by classic gel filtration. When enzymes are studied, active enzyme gel chromatography is a useful alternative. A variant of classic gel filtration is gel filtration equilibrium analysis, which is similar to equilibrium dialysis. When the association formed is only dynamic and equilibrates very rapidly, either the Hummel-Dryer method of equilibrium gel filtration or large-zone equilibrium filtration sometimes allows the interactions to be analyzed, both qualitatively and quantitatively. Very often, however, interactions between enzymes and proteins can only be evidenced in vitro in media that mimic the intracellular situation. Immobilized proteins are excellent tools for this type of research. Several examples are indeed known where the immobilization of an enzyme on a solid support does not affect its real properties, but rather changes its environment in such a way that the diffusion becomes limiting. Affinity chromatography using immobilized proteins allows the analysis of heterologous protein-protein interactions, both qualitatively and quantitatively. A useful alternative appears to be affinity electrophoresis. The latter technique, however, is exclusively qualitative. All these techniques are described and illustrated with examples taken from the literature.

Adsorptive immobilization of submitochondrial particles on concanavalin A Sepharose-4B

Submitochondrial particles (SMPs) prepared from beef liver mitochondria were immobilized on concanavalin A Sepharose-4B (Con A-Sepharose). The process of immobilization was optimized by choosing an appropriate buffer system containing Mn2+ and Ca2+. Adsorption of SMPs on Con A-Sepharose was found to be reversible process, nonelectrostatic in nature, and responsive to the presence of methyl alpha-d-glucopyranose and alpha-d-mannose. The involvement of membrane glycoproteins in the adsorption process was thus demonstrated. Further analysis of the data obtained on competition of binding by sugar molecules provided competition constants reflecting the potency of inhibition by each individual carbohydrate. Positive-cooperative interactions for binding to the matrix were observed especially at high concentrations of SMPs. The immobilized preparations were used successfully in continuous catalytic transformations involving succinate-cytochrome c reductase (SCR) and enzyme complex of the inner-mitochondrial membrane. Best results were obtained when such operations were carried out at 37 degrees C.