84 



H. HALVORSON et al. 



We have recently purified a number of these enzymes present 

 in spores^. Of particular interest was the DPNH oxidase which 

 is the primary route of DPNH oxidation. In Warburg studies 

 with a 20-fold purified enzyme, DPA stimulated oxygen uptake 

 3 fold while FMN stimulated oxygen uptake 9.4 fold. The 

 lack of inhibition of the enzyme by cytochrome inhibitors, as 

 well as the spectrum of the enzyme, suggest a flavoprotein 

 oxidase employing FMN as a cofactor. 



K, =5.5x10" 



1.0 







Atabrine + DPA 



Km =3.1x10"^ 



10 



20 



10 



20 



xlQ- 



4x10" 



Fig. 6. Competitive inhibition of FMN and DPA by atabrine on the soluble 

 DPNH oxidase. Reaction mixtures contained 0.1 M phosphate buffer, 

 pH 7.3, 5 X 10-6 M atabrine, 1 10"^ M DPNH, enzyme, plus FMN and 

 DPA as indicated. Optical density changes were followed at 340 m^ at 25", 



DPA and FMN appear to compete for the same site (Fig. 6). 

 Atabrine, a flavine analog, competitively inhibits the stimulation 

 of DPNH oxidation by either DPA or FMN. The affinity 

 constant for atabrine is essentially the same calculated from 

 both systems. DPA depresses the rate of FMN stimulation, this 

 inhibition being reversed by higher concentrations of FMN. 



DPA thus not only can substitute for FMN in stimulating the 

 enzyme but also competes with FMN for the enzyme. This 

 raises the interesting speculation that DPA, which has the 



