Vicinal dithiol in pig heart mitochondrial F1-ATPase related to thermal or ATP-dependent conformational changes

Active F1-ATPase prepared from pig heart mitochondria can react with about 2 mol of DTNB (5,5'-dithiobis-2-nitrobenzoic acid) or CPDS (6,6'-dithiodinicotinic acid). The reactivity of these thiol reagents decreases if ATP is absent or if F1-ATPase has been submitted to thermal treatment that increases the specific activity without eliminating any contaminating protein. Affinity chromatography on a Sepharose-DTNB column has shown that the thermal treatment of F1-ATPase induces a conformational change of the enzyme that completely prevents it from being retained on the column while the normal active enzyme can be specifically bound to the Sepharose-DTNB column. A comparative study of the thiols of F1-ATPase reacting with CPDS measured by spectrophotometric estimation of the thione released from CPDS and by [14C]CPDS binding to F1-ATPase suggests involvement of a vicinal dithiol in active F1-ATPase. After CPDS reaction, this vicinal dithiol may become an internal disulfide bridge.