PH-dependent changes in mitochondrial membrane structure.

Abstract

The pH-dependent changes in structure of submitochondrial vesicles prepared from rat liver have been investigated by a variety of structural “probes”. The main changes are: (a) the volume of the vesicles as assessed by electron microscopy and packed volume is dependent upon pH, being a minimum at pH 5. Between pH 5 and pH 9 the changes are reversible; (b) the accompanying light-scattering changes are also sensitive to divalent cations; (c) the binding characteristics of 8-anilinonaphthalene-1-sulfonic acid indicate pH-dependent changes in the amount of net charge on the membrane; (d) above pH 4, circular dichroism spectra show alterations characteristic of changes in quaternary protein structure; (e) below pH 4, infrared studies indicate changes in protein secondary conformation are also taking place. From these results, the nature and limits of conformational (molecular) and configurational (morphological) changes in mitochondrial membranes following changes in H+ activity are better defined. In the physiological range, pH-dependent conformational changes are confined to reversible changes in quaternary structure resulting from alterations in membrane charge.