STRUCTUEAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 55 



However, it may be mentioned that rosaniline exhibits metachromasy in the 

 presence of DNA (Lawley, 1956). 



Michaehs (1900) had recommended the supravital use of the dye, Janus 

 green B, as a specific stain for the filamentous cytoplasmic structure now 

 known as mitochondria. This blue dye is a conjugate of the red diethyl 

 safranme through an azo linkage to dimethyl anihne. The nature of the 

 specificity of mitochondrial staining by this dye has been unraveled by 

 Lazarow and Cooperstein (1953). The dye is specifically adsorbed by many 

 proteins; there is no evidence for a specific mitochondrial adsorption. The 

 dye can be dehydrogenated in the following sequence of reactions: 



2H 2H 2H 



Janus green B ^ leuco Janus green B-> diethyl safranine ^diethyl safranine 

 (blue) 02 (colorless) (red) O2 (colorless) 



These conversions are effected by reduced flavoproteins, and, with the 

 exception of the cleavage step leading to the formation of red diethyl 

 safranine, the reactions may be reversed by the oxidation of reduced flavo- 

 protem through cytochrome systems or by molecular oxygen. The dye is 

 initially adsorbed on all parts of the cell. In the absence of sufficient O2, the 

 reductions via FADHg to the colorless stage proceed rapidly throughout all 

 fractions of the cytoplasm. In the mitochondria, which are able to reoxidize 

 reduced intermediates, the reduction to colorless forms is reversed. Staining 

 in the mitochondria does not occur anaerobically in the presence of cyanide 

 (Showacre, 1953). Thus, the mitochondria stain blue in solutions of excess 

 dye and red m dilute solutions, as a result of reductive cleavage to diethyl 

 safranine, while the remainder of the cytoplasm is colorless or slightly pink. 

 Potter et al. (1951) have used this stain to analyze the extent of contamina- 

 tion of mitochondrial preparations. It has been possible to demonstrate that 

 all mitochondria are uniform to the extent that each mitochondrion is able to 

 prevent the irreversible dehydrogenation of the dye. Nevertheless, as will be 

 noted below, other types of biochemical heterogeneity have been reported 

 among these particles. 



3. Mitochondria 



Of the many structures present in animal cytoplasm, we shall discuss only 

 the three major fractions defined by the centrifugal technique described on 

 p. 38, i.e., mitochondria, microsomes, and the clear supernatant fluid 

 remaining after deposition of microsomes at 20,000 g for one hour. As noted 

 above, the first of these was first isolated by Bensley and Hoerr (1934a and b). 

 The isolation of mitochondria was rediscovered when the large granules ob- 

 tamed by differential centrifugation were observed to stain with Janus green 



