GENERAL METABOLISM in vitro 11 



of liver mitochondria (see Schneider, 1944), results in cerebral 

 mitochondrial preparations with a low capacity for oxidative 

 phosphorylation (Brody and Bain, 1952) and a loss of dehydro- 

 genase activity for vital dyes (Showacre, 1953) as compared with 

 preparations made in 0-25 M sucrose. The oxidation of glutamate 

 by mitochondria from cerebral tissues is greatly enhanced by 

 treatment with a chelating agent such as 1 : 10 phenanthroline at 

 10"^ M whereas liver mitochondria are unaffected (Christie et ah, 

 1953). Mitochondria from cerebral tissues carry out a complete 

 oxidation of glucose to carbon dioxide and water (Dubuy and 

 Hesselbach, 1956; Gallagher et al., 1956; see however, Aldridge, 

 1957) a process not occurring in liver mitochondria while octanoic 

 acid, readily oxidized by liver mitochondria, is not oxidized by 

 cerebral mitochondrial preparations (Christie ^^«/., 1953 ; Aldridge, 

 1957). The stability of brain mitochondrial preparations as regards 

 oxidation of pyruvate, is less than that of liver prepara- 

 tions (Aldridge, 1957). Nevertheless, in a suitable medium 

 brain mitochondria respire at a linear rate for periods of up to 

 90 min. 



It is not clear whether mitochondrial preparations from brain 

 contain enzymes from the glycolytic sequence. Thus, Brody 

 and Bain (1952) and Abood et al. (1951) were unable to demon- 

 strate glycolysis in their preparations, a result which has been 

 more recently confirmed by Aldridge (1957). On the other hand 

 the hexokinase of calf brain was found to be associated with 

 particulate material which could be centrifuged from suspension 

 (Crane and Sols, 1953) and the complete glycolysis of glucose to 

 lactic acid has been shown to occur with several mitochondrial 

 preparations (Hesselbach and Dubuy, 1953; Dubuy and Hessel- 

 bach, 1956, 1958; Gallagher et al, 1956). Whether these latter 

 results represent adsorption of enzymes upon particulate material 

 is not known. As noted above, brain mitochondrial preparations 

 are heterogeneous and the discrepancies may be, in part, due to 

 a variable inclusion of particles which are not mitochondria. 



The above constitute the major types of preparations used for 

 the study of metabolism of cerebral tissue. While choice of 

 preparation must be determined partly by the nature of the 

 problem being studied it is to be remembered that the greater the 

 degree of dispersion the less the tissue preparation resembles 

 whole brain and caution is needed in extrapolating results. 



