276 A SYMPOSIUM ON RESPIRATORY ENZYMES 



of isolated enzyme systems has been discussed by Dr. Potter, who 

 pointed out that all precautions must be taken to assure complete 

 restoration of the diffusable factors necessary for the maximal ac- 

 tivity of the enzyme system under consideration. The stimulatory 

 eflFect of calcium upon the succinoxidase system in tissue homo- 

 genates necessitates the addition of calcium to such a system if the 

 maximal activity is to be attained. A dissociable complex involving 

 calcium is indicated. The addition of aluminum ions has been shown 

 by Dr. Potter to overcome an effect resulting from further dilution 

 of the tissue. It thus becomes apparent that when either minced liver 

 preparations or tissue homogenates are employed as the source of 

 the succinoxidase system, it is necessary to add calcium and, under 

 certain conditions, aluminum in order to eliminate these ions as 

 possible limiting factors which may affect the validity of the succin- 

 oxidase assay. 



TISSUE METABOLISM IN VITRO AND IN VIVO 



FREDERICK BERNHEIM 



School of Medicine, Duke University 



The work of Battelli and Stern in the early part of the century may 

 be said to have begun the work on tissue metabolism in vitro which 

 has culminated in the isolation of a number of dehydrogenases. Some 

 of the enzymes which they showed to be present in tissue suspensions 

 have since been shown to be of importance in the economy of the 

 animal. In particular, all subsequent work on the physiology and 

 pharmacology of alcohol has shown that its fate in the body can be 

 accounted for by the activity of the alcohol oxidase of liver which 

 they discovered. Some time later Warburg studied the effect of 

 cyanide on isolated tissues, and from this work came the discovery 

 of cytochrome oxidase and the cytochromes. Again, work on the 

 pharmacology of cyanide has shown that its action on the animal 

 can be explained on the basis of its inhibition of the cytochrome 

 oxidase. In these two early groups of experiments the correlation 

 between in vitro and in vivo results is good. With more recent work 

 sirnilar correlations have either not been made or have not been 

 satisfactor)^ 



The justification for working with broken cell suspensions or cell 

 extracts is that it is only by this means that intracellular enzymes can 

 be studied. The results thus obtained can indicate only that the cell 

 or cell catalyst has certain potentialities under the given set of condi- 

 tions. Under no circumstances are such results in themselves evi- 



