62 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL, SYSTEMS 



placed in a boiling water bath for several minutes. This activation can be 

 seen quite strikingly in figure 1, where the DPN pyrophosphatase activity 

 of the boiled extract is at least 10-15 times that of the unboiled material. 

 It might be pointed out that these enzymes are the only 'heat-activated' 

 ones found thus far in extracts of Proteus. Other enzymes, such as alcohol 

 dehydrogenase and nucleoside phosphorylase are readily inactivated by 

 heating, as one might expect. 



100 



100 



^80- 

 $60 



i 



Q 20 



10 



20 30 40 50 60 

 TIME (Min.) 



10 20 30 



TIME (Min.) 



Fig. 1. Activation by boiling of DPN pyrophosphatase. The enzyme preparation 

 was a 1-6 sonicate of Proteus vulgaris cells in water. Reaction run at pH 7.5 (tris 

 buffer). DPN remaining at given times was assayed by the alcohol dehydrogenase 

 method. (Science 123: 50, 1956.) 



Fig. 2. Effect of inhibitor on DPN pyrophosphatase. The enzyme was an 18-fold 

 purified active pyrophosphatase from Proteus vulgaris. Inhibitor fraction dialyzed for 

 18 hours against distilled water. (Science 123: 50, 1956.) 



DISTRIBUTION OF 'hEAT-ACTIVATEd' ENZYMES 



Having unwittingly stumbled upon this unusual phenomenon in Proteus 

 vulgaris, it seemed of interest to carry out a rough survey to ascertain the 

 extent of this odd reaction in various tissues and microorganisms. The only 

 enzymatic reaction studied was the hydrolytic cleavage of DPN at either 

 the pyrophosphate bond (reaction 1) or at the nicotinamide ribose linkage 

 (reaction 2) where A stands for adenine, R, ribose, P, phosphate, and N, 

 nicotinamide. 



reaction 1: 



reaction 2: 



A-R-P-P-R-N -» A-R-P + N-R-P 



A-R-P-P-R-N -^ A-R-P-P-R 4- N 



