The influence of diphosphopyridine nucleotide on the stability of typhus rickettsiae.

A study of the factors influencing the stability of typhus rickettsiae in vitro, initiated several years ago (Bovarnick et al., 1950), has been extended with the aim of ultimately achieving growth in vitro of these organisms. During these experiments it was noted that survival was increased consistently by addition of diphosphopyridine nucleotide (DPN) to the basal medium. In addition, diphosphopyridine nucleotide increased the rate of oxygen uptake by the rickettsiae with glutamate as substrate. Since both of these effects were relatively small and the diphosphopyridine nucleotide preparations were not pure, it was thought that an impurity might be responsible for the result. Therefore, a sample of diphosphopyridine nucleotide that had been autoclaved to destroy the diphosphopyridine nucleotide itself was tested. Not only was the stimulatory effect removed by this procedure, but the autoclaved diphosphopyridine nucleotide proved to be strongly inhibitory to the survival of the rickettsiae and partially so to their rate of oxygen uptake. This inhibition could be prevented completely by simultaneous addition of untreated diphosphopyridine nucleotide. It is believed that these results indicate that diphosphopyridine nucleotide, or possibly some impurity of equal heat lability, is of considerable importance to the metabolism of the rickettsiae.