INTRACELLULAR LOCALIZATION 



OF SUCCINIC DEHYDROGENASE 



AND DPN-DIAPHORASE AS REVEALED 



BY ELECTRON MICROSCOPY 



D. G. SCARPELLI 



Department of Pathology, Ohio State University, Columbus, Ohio, U.S.A. 



One millimeter cubes of cortical tissue from rat kidney were incubated 

 in média containing Tris buffer {pH 74), 0-44 M sucrose or 7,5 per cent 

 polyvinyl-pyrrolidone, 0-5 mg Nitro BT, 1x10"* M KCN and either 1x10'* M 

 of sodium succinate or redueed diphosphopyridine nucleotide (DPNH) as 

 substrates. Cortical tissue incubated in identical média devoid of sub- 

 strate served as controls. Duplicate experiments were performed in which 

 cell membranes were damaged by freezing and thawing. Amytal was used 

 as a respiratory inhibitor in several experiments in an effort to differen- 

 tiate between intra- and extra-mitochondrial DPN-diaphorase. 



Electron dense deposits intimately associated with intramitochondrial 

 membranes were visualized when sodium succinate was used as the 

 substrate. Incubation in DPNH-containing média, on the other hand, 

 resulted in the visualization of électron dense formazan deposits on the 

 extra-mitochondrial membranous and granular éléments of the cytoplasm 

 and the outer mitochondrial membrane. 



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