82 H. HALVORSON et oL 



first enzyme active on glucose, the DPN-linked glucose dehydro- 

 genase, stimulated by DPA. It was apparent from these findings 

 that DPA was acting in stimulating the electron transport 

 system rather than at the level of substrate oxidation. Since 

 DPA is a powerful chelating agent and heavy metals have been 

 implicated in controlling electron transport in other systems, it 

 seemed not unreasonable that it may be acting here by virtue of 

 its chelating potential. Such mechanism of action was in fact 

 suggested by an analysis of the DPA stimulation of the ATPase 

 of spores^^. The ATPase was slightly inhibited by Mn-~ and 

 perhaps certain other divalent metals present in the spore 

 extract. An experiment designed to test the chelation hypothesis 

 with the soluble DPNH oxidizing system was negative^^. The 

 stimulation could not be attributed to the removal of an 

 inhibitory metal since two other chelating agents, 8-hydroxy- 

 quinoline and versene did not stimulate the enzyme, and prior 

 dialysis against DPA did not abolish the DPA eifect. 



A clearer understanding of the mechanism of DPA stimula- 

 tion has been handicapped by our knowledge of the electron 

 transport system operative in spores. A number of observations 

 have made it clear that it differs in several respects from that of 

 the vegetative cells. Keilin and Hartree-^ reported that spores 

 had less than 6 % of the cytochromes present in vegetative cells. 

 Hachisuka et al.^^ observed similar results and also found that 

 overall germination is characterized by a development in the 

 respiratory system. Spencer and Powell^^, on the other hand, 

 showed that the flavin content does not vary during germination. 

 Nakada et alA^ observed that spores are less sensitive to cyanide 

 than are vegetative cells and that germination is accompanied 

 by cytochrome synthesis. 



These observations led us to a closer examination of the 

 enzymes normally associated with electron transport. A com- 

 parison of some of these in extracts of vegetative cells and in 

 extracts of activated spores^ is shown in Table I. In vegetative 

 cells DPNH oxidation is primarily associated with a particulate 

 system rich in DPNH-oxidizing enzymes and cytochromes. 



