520 BIOCHIMICA ET BIOPHYSICA ACTA SHORT COMMUNICATIONS BBA 43262 Oxidative phosphorylation in yeut VII. Inhibition of oxidative ~lation and of respirmtory enzyme synthesis by oligomycin in intact cells Oligomycin has been an important tool in studies of oxidative phosphorylation in subceUular systems1-3. Additional information can be gained by studying the action of oligomycin at the level of the intact cell. Such a study is presented in this com- munication, complementing data from another laboratory 4. Fig. i shows that respiration of aerobically grown yeast can be inhibited up to 67 % by oligomycin, the inhibition being relieved by uncoupling agents. The extent of the respiratory inhibition by oligomycin has varied considerably (in the range of pL A 4O( 30C 20C 10C ~4 ,/ . ,,A .o3 ,4i 2"" " /' ,o" ,~ ,F 2" 20 40 60 BO 0 p / ,J 20 40 60 80 0 5;~0 t Time (rain) I i t i I 5 0 600 640 x (nm) Fig. I. Effect of oligomycin on respiration of aerobically grown yeast. S. cemvisiae DT XlI was cultured aerobically at 3°0 in a semi-synthetic medium6 with o.25 ~o glucose for 24 h. Respiration was measured manometrically at 3o°. Main compartments of Warburg vessels contained in 2. 5 ml: 80 mM citrate phosphate buffer (pH 4.3), 5° mM glucose and 0.8 mg yeast (dry weight). Inhibitors were used at the following final concentrations: oligomycin, 4° pg/ml (+ I~o methanol); 2, 4- dinitrophenol, 5o pM. Fulllines represent O t consumption, dotted lines CO 2 production. A. 2 and 3, control without oligomycin; i and 4, oligomycin present in the main compartment. At arrow, 2,4-dinitrophenol was added from the side arm. B. At arrow, oligomycin was added from the side arm. Fig. 2. Difference spectra of yeast grown in the presence of inhibitors. The cells grown as described in Table I were washed and suspended in an equal volume of water. Spectra were recorded in the SF io spectrophotometer; sufflmnsion in the reference cuvette was oxidized with 5o mM H=O 2 and in the sample cuvette reduced either with endogenous sulmtrates (in control and in oligomycin- cultured cells) or with IO mM DL-lactate + solid dithionite (in other cases). Biochim. Biophys. Acta, 205 (197o) 52o-523