CARL F. CORI 



microscopy. Several enzymes have been shown to be latent in 

 mitochondria ; this implies either that the enzymes were present 

 in an inactive form or, if active, that they were not in contact 

 with their substrates. Furthermore, the metabolic activity of 

 the mitochondria must be integrated with that of the cell as a 

 whole. The relationship is such that metabolites, e.g., pyruvic 

 acid, prepared by other enzyme systems must be supplied to the 

 mitochondria as oxidizable substrates, while the cell must in 

 turn be supplied with ATP which is being regenerated in the 

 mitochondria. The functioning of the cell depends to a large 

 extent on this interrelationship. 



The complexity of the system consists not only in the large 

 number of diverse chemical operations which are carried on 

 simultaneously in the same cell but also in the control of the 

 speed of these operations. One might speculate that the neces- 

 sary catalysts for a particular operation are associated into a 

 unit within the cell. For example, hexokinase, phosphogluco- 

 mutase, and phosphorylase in loose combination, perhaps in a 

 separate compartment in the cell, would be a unit for glycogen 

 synthesis, while other molecules of phosphorylase and phospho- 

 glucomutase in combination with glucose-6-phosphatase would 

 form a unit for glycogen degradation in the liver. Glucose-6- 

 phosphatase, according to DeDuve et al. (7), is bound to the 

 microsomes. Although phosphorylase and phosphoglucomu- 

 tase appear to be present in a soluble form in a liver homogenate, 

 this does not exclude loose combinations which would be 

 broken up by present methods used for the disintegration of 

 cells. Crane and Sols (4) have shown that over 90 per cent of 

 the hexokinase in a brain homogenate is bound to particles 

 which sediment at relatively low centrifugal speeds and which 

 resemble mitochondria, whereas homogenates of other tissues 

 contain a considerable part of hexokinase in soluble form. No 

 information is available at the present time as to whether these 

 findings have any physiological meaning. It would seem that 

 new methods will be needed to explore this territory. 



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