Effects of polycationic proteins on mitochondrial structure and function



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Basic proteins, such as histones, protamines, poly lysine, and parathyroid hormone, cause an extrusion of K+ and low-amplitude swelling in isolated mitochondria. These effects are dependent upon an energy supply, either substrate oxidation or ATP hydrolysis. The results suggest that a high- energy intermediate common to both electron transport and phosphorylation is involved in the polycationic protein effects. A stimulation of respiration and ATP hydrolysis is associated with K+ extrusion and swelling. These effects of the basic proteins are facilitated by the presence of permeant anions and inhibited by the divalent cations Mg++, Mn++, and Sr++ and by local anesthetics such as dibucaine. A mechanism is presented which involves the interaction of the basic proteins with a K+ carrier in the mitochondrial membrane, leading to energy-dependent conformational changes in the carrier and a release of bound K+. These studies indicate the possible significance of basic proteins in controlling mitochondrial function. In addition, the polycationic proteins are convenient tools for examining the processes of ion transport and swelling in mitochondria and for studying the nature of polyelectrolyte interactions with membranes in general.