Opposing actions of Ca++ and ATP plus Mg++ in controlling the kynurenine aminotransferase activity of isolated rat kidney mitochondria

Abstract

A new method of monitoring changes in the permeability of the mitochondrial inner membrane to substrates, based on mitochondrial kynurenine aminotransferase activity, is applied in this study of a requirement for Ca++ for optimal translocation. At pH 7.25, the Ca++ requirement was satisfied by endogenous (non-added) Ca++. The endogenous activity was decreased by 1.4 mM SrCl2, MnCl2, MgCl2, BaCl2, and LaCl3 and was unaffected by 1.4 mM NaCl, KCl, and NH4Cl. It was depressed to a minimum by 70 [mu]M EGTA and rapidly restored by 70 [mu]M CaCl2. The restored level was again depressed (rapidly) by added ATP + Mg++. The observations are discussed as a possible reflection of a known role of the Ca++/Mg++ ratio in determining mitochondrial membrane permeability.