The mitochondrial adenosine triphosphatase complex : studies on the interaction between its catalytic and H⁺-translocation components

• The aim of the present investigation was the characterization of the mitochondrial adenosine triphosphatase complex, with respect to its subunit composition and to the function of the individual components in the interaction between the catalytic and H+-translocating processes catalysed by this enzyme.The enzyme consists of two structurally and morphologically different units: a hydrophilic part Fl, the centre for the catalysis of the hydrolysis and synthesis of ATP, and a membrane part Fo, which constitutes a binding site for Fl and mediates the translocation of protons through the membrane.The composition of Fo has been studied using sodium dodecylsulphate gel electrophoresis; the results indicate that Fo consists of five Coomassie blue-stainable components of molecular weights of 23 000, 21 000, 10 500, 9 400 and 8 600; components of molecular weights of 21 000 and 9 400 correspond to "oligomycin sensitivity conferring protein" (OSCP) and "coupling factor 6" (F6). Two bands not stained with Coomassie blue were detected by autoradiography of the gels of Fo preincubated with [14C]-dicyclohexylcarbodiimide. These two bands of molecular weights of about 18 000 and below 6 500 represent monomeric and oligomeric forms of the dicyclohexylcarbodiimide-binding protein. The function of Fo as a protonophore has been documented by incorporation of Fo into liposomes and demonstration of its protonophoric activity by release of a K+-induced proton gradient through the membrane.Qualitative and quantitative aspects of the binding of Fl to isolated Fo have been investigated. The OSCP and F6 components of Fo, mediating its interaction with Fl, have been proposed to constitute separate links between the proteolipid component of Fo and Fl.The oligomeric structure of the dicyclohexylcarbodiimide- -binding component of Fo has been investigated. The stoichiometries and kinetics of the effect of oligomycin and dicyclohexylcarbodiimide on ATPase activity and related reactions have been studied. The results differentiate the effects of the two inhibitors and indicate a high degree of complexity of the system.

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NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

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