56 S. S. COHEN 



B (Hogeboom et al, 1948). When isolated by the sucrose technique, 

 these granules often had the rod-shaped appearance of mitochondria in 

 cells. 



The particles, xasible in the light microscope, have a considerable degree 

 of variabihty, being filamentous, spherical, or vesicular. In the resting cell 

 their diameter is about 0.5 and 1/x, with 0.2 and 2n. as extremes, and a maxi- 

 mum length of 7jLt. Observations with the electron microscope, notably by 

 Palade (1953, 1955) and Sjostrand (1953), have revealed that mitochondria 

 have a characteristic organization, whether derived from plant or animal 

 material.^ They possess a surface membrane and internal compartments 

 separated by lamellae, termed "cristae mitochondriales." The laminated or, 

 occasionally, tubular cristae show degrees of branching, which vary from 

 cell type to cell type, and it is suggested that the purpose of the infolding is 

 to increase internal surface rather than compartmentalization. Most often 

 the lamellae are perpendicular to the long axis of the organelle and appear to 

 be more or less parallel to one another, as presented in Fig. 3. In sections of 

 mitochondria one may readily see that the surface membrane consists of 

 2 parallel membranes, each about 50 A thick, and that the inner membrane 

 connects with the one end of the cristae mitochondriales, which project 

 finger-like within the mitochondrion. Within the imier chamber of the particle 

 is a relatively homogeneous dense material, which occasionally contains 

 smaU granules of high density. 



The preservation of the fine structure of mitochondria in the process of 

 isolation is a relatively recent event, made possible by a careful control of 

 the isolation procedure by electron microscopy (Novikoff, 1956). The isolation 

 technique of choice has required the use of h3rpertonic solutions at defined 

 pH in order to prevent the swelling of the mitochondria. In tte early isola- 

 tions of mitochondria by Claude (1946), it was observed that handling or 

 storage in hy^Dotonic solutions resulted in a rapid disintegration or lysis. 

 Dense submicroscopic granules containing ENA could be isolated from such 

 a lysate. In the earhest isolations of "cyclophorase" or mitochondria, studied 

 by Green and his collaborators as an approach to the integration of the citric 

 acid cycle, fatty acid metabolism, etc. (Green, 1951, 1957), it was soon 

 observed that the particles developed coenzyme requirements in the course 

 of handling or mishandling. There appears no reason to doubt that the 

 subsequently observed release of coenzymes and the ready diffusion into the 

 particle of exogenously supplied coenzyme were consequences of the swelHng 

 or lysis of a semipermeable mitochondrial membrane (Lindberg and Ernster, 

 1954). A comparable case was studied by Berthet et al. (1951), who observed 

 the exposure and release of acid phosphatase by mitochondria after exposure 



1 A particle of similar size, organization, and enzymatic constitution has never been 

 observed in bacteria. 



