SOLUBILIZATION AND PROPERTIES OF THE DPNH DEHYDROGENASE llj 



TABLE IV 



Effect of Known Inhibitors of DPNH-Cytochrome Reductase on Cyto- 

 chrome c Reduction by DPXH Dehydrogenase 



Inhibitor Inhibition ("„) 



PO4, o-oi M 78 



Pyrophosphate, o-oi M 85 



Ca^ ^, 001 M 78 



Mg~ ^, 001 M 76 



Conditions: as per Mahler and Elowe [25]; assay at pH 8-5. 



flavoproteins after solubilization rather difficult. In the present work this 

 difficulty was circumvented by the expedient of using a starting material 

 known to contain only one DPXH oxidizing activity, the flavoprotein 

 attached to the respiratory chain. 



Assuming that the assay conditions are not too dissimilar, the best 

 preparation hitherto obtained in the Detroit laboratory is some eighty to 

 ninety times more active than the purified enzyme described by King and 

 Howard [7]. The major differences between their preparation and ours 

 are that while theirs is very unstable, ours is quite stable ; their preparation 

 precipitates at a considerably higher range of (NH4)2S04 concentrations 

 than does ours [7] ; and, finally, that while our enzyme is so thoroughly 

 adsorbed on DEAE cellulose as to render fractionation on this exchanger 

 quite unfeasible, theirs is readily eluted from DEAE cellulose [28]. These 

 differences seem too great to be readily accounted for by the different 

 degrees of purification of the two preparations and, hence, at this time it 

 is uncertain whether the two laboratories are indeed investigating the 

 same enzyme. 



References 



1. Stravib, F. B., Biochem.J. 33, 787 (1939). 



2. Mahler, H. R., Sarkar, N. K., and Vernon, L. P., and Alberty, R. A.J. binl. 

 Cheni. 199, 585 (1952). 



3. Ziegler, D. M., Green, D. E., and Doeg, K. A., J. bio!. Chem. 234, 1916 



(1959)- 



4. Massey, \., Biochini. biopJiys. Acta 37, 310 (i960). 



5. Massey, V., Biochim. biophys. Acta 38, 447 (i960). 



6. Massey, V., Biochim. biophys. Acta 37, 314 (i960). 



7. King, T. E., and Howard, R. L., Biochini. biophys. Acta 37, 557 (i960). 



8. Singer, T. P., Kearney, E. B., and Bernath, P., J. biol. Chcni. 223, 599 (1956). 



9. Ringler R. L., and Singer, T. P., Biochim. biophys. Acta 29, 661 (1958). 



10. Ringler, R. L., Minakami, S., and Singer, T. P., Biochem. biophys. Res. Comm. 

 3, 417 (i960). 



11. Crane F. L., Glenn, J. L., and Green, D. E., Biochim. biophys. .4cta 22, 475 

 (1956). 



