507 



Anthony San Pietro, Leo P. Vernon and Dorothy Limbach 



light- trapping system and ascorbate as the hydrogen donor. If one assumes 

 that this system functions in a manner analogous to the chloroplast system, 

 then the transhydrogenase must catalyze a transfer of electrons from an 

 activated form of hematoporphyrin to NADP, It would thus appear that in 

 this soluble system transhydrogenase can interact directly with the activated 

 hematoporphyrin without the intervention of PPNR. In the chloroplast system 

 there is no direct interaction of the transhydrogenase and activated chloro- 

 phyll; the interaction between them is mediated by PPNR. The difference 

 between these two systems is most probably due to the fact that one is a 

 soluble system and the other is a particulate system with a very high degree 

 of organization. 



Recently, Smillie ^^^' has reported the isolation of a flavoprotein from 

 Anacystis nidulans which exhibits PPNR activity. This flavoprotein will sub- 

 stitute for either spinach or Anacystis PPNR in a number of reactions which 

 were thought to be specific for PPNR. There is some similarity between the 

 data presented here and that reported by Smillie ^ ' but any possible signifi- 

 cant relationship between them must await further experimentation. 



It should be noted that the hematoporphyrin system exhibits specificity 

 for the transhydrogenase flavoprotein as does the chloroplast system. 

 Lazzarini and San Pietro ^^'^' have isolated another flavoprotein from spinach 

 which exhibits TPNH-diaphorase activity but no transhydrogenase activity. 

 This flavoprotein did not substitute for the transhydrogenase flavoprotein in 

 this system. 



This research was supported in part by a grant (GM- 10129) to one of us 

 (A. S. P. ) from the National Institutes of Health, United States Public Health 

 Service, 



This is Contribution No. 130 from the Charles F. Kettering Research 

 Laboratory. 



BIBLIOGRAPHY 



1. Krasnovsky, A. A., Doklady Akad. Nauk S. S. S. R. , 60, 421(1948). 



2. Krasnovsky, A. A. , and Brin, G. P. , Doklady Akad. Nauk S. S. S. R. , 



67, 325 (1949). 



3. Brin, G. P., and Krasnovsky, A. A., Biokhimiya, 24, 6(1959). 



4. Krasnovsky, A. A. , and Brin, G. P. , Doklady Akad. Nauk S. S. S. R. , 



73, 1239 (1950). 



5. Krasnovsky, A. A. , and Umrikhina, A. V. , Doklady Akad, Nauk 



S. S. S. R. , m, 1061 (1958). 



6. Vernon, L. P., Acta Chem. Scand. , JL5, 1651(1961). 



7. San Pietro, A., and Lang, H. M. , J. Biol. Chem., 231, 211 (1958). 



8. Keister, D. L, , San Pietro, A. , and Stolzenbach, F. E. , Arch. 



Biochem. Biophys. , 98, 235 (1962). 



9. Keister, D. L. , San Pietro, A., and Stolzenbach, F. E. , J. Biol, Chem., 



235, 2989 (1960). 



