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.This work is part of the Doctorat de Spécialité of A. Di Pietro (Lyon, 1975) and of B. Blanchy (in preparation). It has been partly presented at the Venice Joint Meeting, Venice, October 1976.