EFFECTS OF THYROXINE AND RELATED COMPOUNDS ON LIVER MITOCHONDRIA 1 9 



antimycin A. A further valuable property of this preparation was that it 

 also contained the external type of DPNH-cytochrome c reductase, known 

 to occur in liver mitochondria and characterized by an insensitivity to 

 amytal and antimycin A [38, 39, 47, 91-95]. 



IOOL 



02(+cytc) 



DCPIP 



0.05 



D-?sanrtmof hyroxine ,mM 



0.1 



Fig. 9. Effect of desaminothyroxine on the oxidation of DPNH by various 

 electron acceptors in mitochondrial fragments prepared according to Kielley and 

 Kielley [Ho]. All assay systems contained 0-02 M phosphate buffer, pH 7-5, and 

 Q- 1 m.M DPNH, in a final volume of 3 ml. In the case of O2 as acceptor, either no 

 further additions were made (line marked "O.,"), or 0-005 iri.M cytochrome c was 

 added (" O., ( + cyt. c.) "), and the oxidation of DPXH was followed at 340 m/x. In 

 the case of 2,6-dichlorophenolindophenol ("DCPIP") as terminal electron 

 acceptor, the dyestuff was added in a final concentration of 0-04 mM, and its reduc- 

 tion was followed at 600 m/t ; in the case of cytochrome c (" cyt. c ") this was added 

 in a final concentration of 0-05 mM, and its reduction was followed at 550 m/x. 

 In both latter cases, 0-33 mM KCN was included in the test. " loo^^o activity" 

 was (in terms of /xmoles DPNH oxidized /min. per g. liver): 0-146 with O.., 

 0-218 with 0._, (+ cyt. r), 0-620 with cyt. r, and 0-487 with DCPIP as electron 

 acceptor. 



As can be seen in Fig. 9, desaminothyroxine greatly inhibited the 

 DPNH oxidase activity of the Kielley and Kielley preparation as measured 

 without added cytochrome r, as well as the diaphorase activity as measured 



