Asymmetry of the Mitochondrial Inner Membrane

Abstract

<p> The mitochondrial inner membrane is highly selective with regard to permeability to solutes and the movement of a large number of large or charged molecules across it therefore requires specific transport processes provided by specific membrane proteins. </p> <p> In order to study the spatial arrangement of one such protein the adenine nucleotide translocator protein which transports ADP and ATP across the mitochondrial inner membrane, a number of chemical labelling studies of the mitochondrial inner membrane were carried out. </p> <p> Mitochondrial inner membrane preparations of normal (mitoplasts) and inverted (submitochondrial particles) config~ration with respect to mitochondria have been isolated and the external phosphatidylethanolamine and proteins modified by 3H isethionyl acetimidate. An upper limit of 40-46% of the total PE in mitoplasts was found to be located in the external monolayer. </p> <p> Differences in protein labelling patterns of isethionyl acetimidate modified mitochondria and SMP was observed. JAI was found to penetrate the outer membrane but not the inner membrane of intact mitochondria. </p> <p> A tritiated photoreactive phospholipid, 1 palmitoyl-2-(mdiazirinophenoxynonanoyl) phosphatidylcholine (DAP-PC) was incorporated into mitoplasts and submitochondrial particles symmetrically into both monolayers by sonication and asymmetrically using phospholipid exchange protein isolated from beef heart. Photolysis yielded the translocator as a major crosslinked product in both types of particles and with both methods of incorporation. </p> <p> It was shown that the adenine nucleotide translocator can be asymmetrically labelled by modification of membrane.particles of opposite orientation by water soluble and membrane soluble probes. </p>