DORMANCY OF BACTERIAL ENDOSPORE 



85 



pyridine ring structure in common with DPN, may act as a 

 cofactor. If it were, one would expect that an enzyme-bound 

 reduced form of DPA was formed. An intermediate of this 

 type. dihydrodipicoHnic acid, has recently been postulated by 

 Powell and Strange-^^ who suggested the following mechanism 

 for the synthesis of DPA from diketopimehc acid (Fig. 7). 



H2C^ CH2 NH3 



c c 



HOOC^ \, o^ ^COOH 



HC XH 



.C C 



HOOC-^ ^N-^ N:OOH 



H 



Qoinone 



CH 



Bacterial enzyme 



HOOC' 



^N^' 



,C 



-COOH 



a,£-Diketopimelic acid 



Dihydrodipicolinic acid 



Dipicolinic acid 



Fig. 7. Pathway of dipicolinic acid synthesis. 



Assuming that DPA can act as an electron acceptor it 

 provides an explanation for a number of phenomena associated 

 with dormancy : 



(1) Burst in respiratory activity of sporulation associated 

 with DPA synthesis'*^; 



(2) Anaerobic germination where it may act as an electron 

 sink substituting for oxygen^-; 



(3) Rise in respiration following activation and germination^^ 

 by stimulating the soluble oxidase pathway-'- ^^. 



THE MECHANISM OF L-ALANINE UTILIZATION 



In the light of the previous discussion it is evident that the 

 DPA-accelerated oxidation of pyruvate or products of pyruvate 

 is essential to germination. The prominent role played by 

 L-alanine can be understood since it represents one of the most 

 direct precursors of pyruvate among the germinating agents. 

 The primary event in the interaction of L-alanine with activated 

 spores has thus far remained obscure. In principle, this could be 



References p. 94 



