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et an 'at'airS de 3fgdeefne, 38~xlj,Grenobte, Fra~.ce Reeei~-ed 13 February 1973 M'ay ]97~1. ]e:r~cluc~ion Adrenal cortex mitochondria are able to catalyze ai least two reactions m the conversion of cholesterol ~o corfico~erone, namely the s~hor~ening of ~he iso. oc/yl chain of cholesterol and e~e hydroxy]at~on al (7-1 I. These reactions are located in ~he inne~ meml~rane ma~r~ ~pace of mitochondna I1--3] and require a mixed N~acd.en oMdation system fo:r which NADPH is the donor" of reducing equNalents. Since ~e inner mitochon&ial membrane is impermeable m pyr~fline nnc]eotides t4] lhe enzymatic reduction of NADP mus~ occur witNn ~he matrix space. Th~s could be ½ough.~ about by NADP linked dehydmgenases present in adrenal cortex mitochondria (NADP isocitrmv dehydrogenase foI tat mi~ochondria and NADP malate dehydrogenase for beef mi~oehondria f5]), if an adequate supply of substrata is rnainiained. One may ask ~erefole whether adrenal cortex mitochondlia, simSlady ~o liver miloehondna possess ~ransport systems for cilrie acid cycle Ntermediates ~o ensure the entry of spec~.c subs'tra~es fo,s NADP dehydrogenases. The present paper provides experimental e~idenee for ~he presence of mull'to, sueemate and oxoglutarale cr~riers in beef adrenal cortex mitochondria. A preliminary account of this work has been communicated 16]. Materials and methodsBeef adrenal cortex rnitochondria were prepared as pre,~iously described I2] m a medium con~taining The reduction of Ntr ~amitoch0ndrial pyridh~e nuc!eetides was assayed w~h a double beam sp~clropho~ome~er m 340-374 nm [7]. In ehis assay, ~i~ochondria were deple.~ed of endogenous pyridine nu.fle,:nides by a pre~ incubation ,~ith FCCP (cmbony~ cyanide pqrffluo~o-methoxyphenyi hydrazone) and ~hen supplememed wi~h romnoue ~o block the respiratory chain.Mffoehondri~d swening was fol!,~wed by ligh~ sca~er-ing chan~;es as described by Chappell and Crofts [8]..'Fne variation of e~;*rar4ag~ochondria~ pH corresponding ~o ~he uptake of me]ate was moJ, i.~o;ed poientiome~ric-lily Using a fast responding low ~esi~ta~ce ~a~ electrode 0ngold) and a radiome~ter pit-meter connected ~o a S.e~Totrace recorder, 7he ~echnique used for incarnating ~he kinetics of anion uptake was/hal described by Quagl~ariello etal. ~9]. ~ he upw, d