THE CYTOPLASM 219 



in the microsomal fraction. Instead, they were largely recovered in the 

 mitochondrial fraction, and it was therefore concluded that their associa- 

 tion with mitochondria was not an artifact. ^^ 



Beinert,^^ in somewhat similar experiments, has shown that the mito- 

 chondria of liver homogenates prepared in water are capable of adsorbing 

 large amounts of cytochrome c. When the homogenates were prepared in 

 0.25 M sucrose, however, the mitochondria adsorbed only small amounts 

 of cytochrome c. These results are of interest in view of the previous find- 

 ing that the cytochrome c of mitochondria was inactive in the succinoxi- 

 dase system when the particles were isolated from liver homogenates pre- 

 pared in water^** but was active when the mitochondria were isolated from 

 homogenates prepared in isotonic saline^* or in 0.25 M sucrose.^* 



b. Biochemical Properties of Isolated Liver Mitochondria 



Tables II to IV list the enzymes and related compounds that appear, 

 on the basis of investigations carried out in a number of laboratories, to be 

 localized in mitochondria. In the case of each enzyme or compound studied, 

 values are included indicating both the per cent recovery in the mitochon- 

 drial fraction and the concentration in the mitochondria as compared with 

 that in the whole tissue. Specific activities are also included to permit a 

 comparison of the activities of the various enzymes investigated. References 

 to the values in the tables are indicated in the left-hand column, and ad- 

 dtitional experimental work pertinent to the results is referred to in the 

 right-hand column. For reasons discussed above, a considerable mass of 

 data appearing in the literature and obtained in incomplete investigations 

 has not been included. When considered to be of cytochemical significance, 

 the latter studies have served more to confuse than to contribute to the 

 issue. In general, they fall into one or more of four categories: (1) investi- 

 gations in which enzymes or compounds were found in relatively low con- 

 centrations in mitochondria; (2) studies of isolated mitochondria without 

 reference to the whole tissue or to other cell fractions; (3) studies of heter- 

 ogeneous particulate preparations that include nuclei, nuclear fragments, 

 mitochondria, and microsomes; and (4) experiments in which an enzyme 

 supposedly under study may not have been the rate-limiting component 

 of the reaction mixture. In this connection, it should be pointed out specifi- 

 cally that a number of extremely informative biochemical investigations, 

 aimed at studying the mechanism of complex enzymic reactions rather than 

 the distribution of enzymes within the cell, have been carried out with 

 either isolated mitochondria or heterogeneous particulate preparations 

 as a convenient source of enzyme. The broad cytochemical implications 



S3 H. Beinert, J. Biol. Chem. 190, 287 (1951). 



5" W. C. Schneider, A. Claude, and G. H. Hogeboom, J. Biol. Chem. 172, 451 (1948). 



