In order to determine the steps with which the reaction of neotetrazolium chloride reduction conjugates in the terminal electron transport system, an analytical study on the neotetrazolium reduction by tissue homogenates was carried out using various substrates such as sodium succinate, p-phenylenediamine, sodium malate, sodium α-glutamate and DPN, and inhibitors such as sodium malonate, potassium cyanide and antimycin A, as the results the following conclusions were drawn. 1. The reaction of neotetrazolium reduction by tissue homogenate
using sodium succinate as substrate is mainly the succinoxidase system reaction; and the reaction takes place conjugating about 50 per cent in the step of the succinic dehydrogenase system (succinic dehydrogease, cytochrome b and cytochrome C1), of these about 15 per cent conjugates in the step prior to the antimycin A sensitive step and 35 per cent in the step itself; and about 50 per cent in the step of cytochrome c oxidase. 2. In the case using p-phenylenediamine as substrate the reaction of neotetrazolium reduction is the reaction due to the activity of cytochrome c-cytochrome oxidase system; and when p-phenylenediamine is used with the sufficient amount of cytochrome c, the reaction appears to be dependent on cytochrome c oxidase activity. Neotetrazolium reduction in all these reactions takes place conjugating in the step of cytochrome c oxidase. 3. In the case where DPN and substrates taking DPN as a coenzyme are used, the reaction of neotetrazolium reduction is mainly the reaction
conjugating at the step below antimycin A sensitive step in the DPNHcytochrome c reductase system (flavoprotein, cytochrome b and cytochrome c;), probably with the flavoprotein of DPNH-dehydrogenase. 4. Endogenous dehydrogenase reactions are the sum total reactions conjugating at the steps prior to the antimycin A sensitive step in the terminal electron transport system and with other various reduction systems which are not inhibited by antimycin A.</p
