140 



LIGHT AND LIFE 



300 340 380 420 460 

 WAVELENGTH (m/J) 



Fig. 22. The absorption spectrum of the pyridine nutleotide complex of the 

 microsomal cytochrome-h-, reductase. Cur\cs 1, 2, and 3 are the absorption bands 

 of 0.8, 1..5, and 3 /iM DPNH. Curves 4, "), and 6 are difference spectra of 3 

 jttM enzyme plus 0.8, 1..5, and 3 /xM DPN respectively, after reduction with ADH 

 and ethanol minus the corresponding spectra before reduction. From Stritt- 

 niatter (20). 



action with the essential thiol group and Avould be like that produced 

 in liver LDH-DPN by sulfide or hydrosulfide ion (29) . It does not 

 resemble the 365 ny band ol GPD-DPN. Since the bound flavin 

 must be in the reduced form in the pyridine nucleotide complex, a 

 reasonable alternative is that the interaction is not with thiol but 

 with a nitrogen atom of the reduced flavin. 



This work was supported in pan l)\ a research grant hoin the National Heart 

 Institute. National Institutes of Health. Some of the work on cocn/ymc conforma- 

 tion in enzyme complexes was initially descrii)ed at the Symposium on Physical 

 Methods in Hiochemislry at the Federation meetings, .Atlantic City, .\pril, 19.50. 

 Kxpcrimcntal details are in press elsewhere. 



