Solubilization and Properties of the DPNH 

 Dehydrogenase of the Respiratory Chain* 



Thomas P. Singer 



Edsel B. Ford Institute for Medical Research, Henry Ford Hospital, Detroit, 



Mich., U.S.A. 



Although the work of our laboratory for the past few years has been, 

 in the main, concerned with the systematic isolation and detailed study of 

 the various dehydrogenases which are structural and functional com- 

 ponents of the respiratory chain, until recently we have not attempted to 

 isolate one of the most interesting enzymes in this group, the respiratory 

 chain-linked DPNH dehydrogenase. One reason for this was the large 

 number of preparations of mitochondrial origin described in the literature 

 which are capable of oxidizing DPNH under suitable conditions. A closer 

 study of the relevant literature reveals, however, that few of these prepara- 

 tions have been well characterized ; even fewer could be ascribed a definite 

 function in cellular metabolism, and no soluble, purified preparations 

 could be assuredly identified with the enzyme which links the oxidation 

 of DPNH to the respiratory chain. 



Among animal tissues heart mitochondria appear to have been most 

 intensively studied with respect to DPNH oxidation. Limiting this dis- 

 cussion to soluble enzymes, free from respiratory chain components, there 

 have been two relatively well-defined preparations isolated from heart 

 mitochondria: Straub's diaphorase [i] and Mahler's DPNH cytochrome 

 reductase [2]. Both of these enzymes have been thought, one time or 

 another, to be artifacts of isolation, a view based on the harsh methods 

 employed in their isolation. As to Mahler's enzyme, the group at the Enzyme 

 Institute still believes that it is an artifact [3], since the peculiar properties 

 of its flavin group may be reproduced by applying the alcohol treatment 

 used in its isolation to other preparations, although JMassev has produced 

 considerable evidence to indicate that the enzyme in fact pre-exists in 

 mitochondria [4]. In either event there is little in its properties that would 

 suggest that it is the flavoprotein component of the DPNH oxidase chain. 



* Supported by grants from the National Heart Institute, National Institutes 

 of Health and the American Heart Association, Inc., and by contract No. Nonr 

 1656 (00) between the Office of Naval Research and this Institute. 



