230 GEORGE H. HOGEBOOM AND WALTER C. SCHNEIDER 



shown that the cytochrome oxidase/^^"^^^ succinic dehydrogenase, ^^^ DPN- 

 cytochrome c reductase/^^ and a-glycerophosphate dehydrogenase"^ of 

 yeast cells are associated with sedimentable particles that may be homo- 

 logues of animal mitochondria. Of interest is the fact that in a mutant 

 strain of yeast cells ("petite colonie""-) characterized by the total absence 

 of respiration sensitive to KCN, these particulate-bound enzymes are lost, 

 whereas other enzymes found in the soluble fraction of normal yeast cells 

 are partially or completely retained.""-"^ 



d. Biochemical Investigations Relating to the Structural Organization of 

 Mitochondria 



A number of interesting properties of mitochondria have been disclosed 

 by biochemical investigations in which the mitochondrial membranes 

 have been either altered by exposure to hypotonic solutions or actually 

 disrupted by mechanical means. When, for example, a suspension of mito- 

 chondria is exposed to sonic oscillations (9 kc. per second) at a low tem- 

 perature for periods up to 30 minutes, essentially all the particles are dis- 

 rupted, leaving an opalescent, brownish-yellow preparation that is optically 

 empty in the light microscope. If the preparation is centrifuged for 30 

 minutes at high speed (40,000 to 50,000 r.p.m. in an angle rotor), approxi- 

 mately 60% of the original total nitrogen is recovered in a clear, highly 

 colored supernatant and the remainder in a transparent brownish pellet. *^"^^ 

 Examination of the latter particulate material in the analytical ultracen- 

 trifuge has revealed that it is polydisperse but does contain several ap- 

 parently discrete components with sedimentation constants of 25 S. (Sved- 

 berg units) or greater,^" Most of the nitrogen in the supernatant represents 

 proteins having sedimentation constants of from approximately 4 to 12 

 g 89,90 ^ typical refractive index pattern obtained in the analytical ultra- 

 centrifuge with the soluble proteins of rat liver mitochondria is shown in 

 Fig. L4. Much of the total protein appears as a symmetrical peak Avith a 

 sedimentation constant of 6.3 S. In addition, there is a trailing peak (S = 

 ca. 4) that appears to be polydisperse, as well as a rapidly sedimenting com- 

 ponent (*S = ca. 12) that is present in relatively low concentration. An 

 identical pattern was obtained with the soluble proteins of mouse liver 

 mitochondria.^' Attempts to fractionate the mixture at low temperature 

 with ethanol in the presence of buffer at low ionic strength disclosed an- 

 other component (S = ca. 5) that is apparently masked by the main com- 

 ics H. Chantrenne, Enzymologia 11, 213 (1943-45). 

 '6' P. P. Slonimski and B. Ephrussi, Ann. inst. Pasteur 77, 47 (1949). 

 I'fl H. E. Hirsch, Biochim. et Biophys. Acta 9, 674 (1952). 

 '^1 P. P. Slonimski and H. E. Hirsch, Compt. rend. 235, 741 (1952). 

 "* B. Ephrussi, Harvey Lectures 46, 45 (1950-51). 



