M. N. SWARTZ, N. O. KAPLAN AND M. E. FRECH 63 



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Mycobacterium butyricinn (8), Bacillus subtilis, Proteus morganii, Pro- 

 teus rettgeri, and Staphylococcus aureus- contain similar enzymes, whereas 

 30 other microorganisms tested do not exhibit this phenomenon. The 'heat- 

 activated' enzymes from Mycobacterium and Bacillus subtilis carry out 

 reaction 2 and are true DPNases. Kern (8) has shown that the DPNase of 

 Mycobacterium is not inhibited by high concentrations of nicotinamide 

 and does not carry out the exchange reaction between the nicotinamide 

 moiety of DPN and isonicotinic acid hydrazide. The enzymes isolated 

 from the other organisms mentioned above appear to carry out reaction 

 1 and are organic pyrophosphatases. It is quite remarkable that this num- 

 ber of truly heat-stable enzymes exists, since the screening for the 'activa- 

 tion' was carried out by actually boiling sonic extracts of the organisms. 

 As yet, a search for 'heat-activated' proteinases, sulfatases or /S galactosi- 

 dases has not been rewarding. 



Thermophilic bacteria, such as Bacillus stearothermophilus studied by 

 Hutner et al. (2) , would perhaps be a likely source of similar enzymes, but 

 as yet we have no information in this regard. Bacterial spores might be 

 another prospective source (9). Stewart and Halvorson (11) have pre- 

 sented evidence supporting the thermostable-enzyme theory for thermo- 

 philism. A racemase which they obtained from spores of B. terminalis 

 remained active after exposure to 80°C for 2 hours, whereas the correspond- 

 ing enzyme prepared from vegetative cells was almost completely inacti- 

 vated in 15 minutes at the same temperature. 



It is interesting to speculate on the possible relationship of the phe- 

 nomenon of 'heat-activation' to the so-called 'temperature mutants'. In 

 general these mutants of Neurospora have little or no activity of a given 

 enzyme when grown at about 35°C whereas at 25°C active enzyme is 

 present (6, 13). However, Yanofsky has found a 'temperature mutant' of 

 Neurospora which grows without added tryptophane at temperatures of 

 30°C or above, but requires this amino acid for growth at lower tempera- 

 tures (14). Extracts of this particular mutant, tdoi , are the only ones 

 from a group of 25 mutants at the td locus, which contain tryptophane 

 synthetase activity. Perhaps it is possible that the growth, without added 

 tryptophane, at the higher temperature is related to the destruction, at that 

 temperature, of an inhibitor of tryptophane synthetase. 



Thus far none of the higher plant or animal tissues that have been in- 

 vestigated have shown heat-activated DPNases or DPN pyrophospha- 

 tases. Most of the information concerning 'heat-activated' enzymes re- 

 lates to Mycobacterium (8) and Proteus (12) and the following discussion 

 will concern the enzymes from these sources. 



-The work on Staphylococcus aureus has been carried out by Mr. A. Mildvan in 

 Dr. A. G. Osier's laboratory. 



