MECHANISM OF 'HEAT ACTIVATION' OF ENZYMES^ 



Morton N. Swartz, Nathan 0. Kaplan and Mary E. Frech, 

 Massachusetts General Hospital, Boston, Massachusetts, 

 and McColliim-Pratt Institute, The Johns Hopkins 

 University, Baltimore, Maryland 



X HERE ARE at least two distinct situations in which the phenomenon of 

 'heat activation' of an entirely inactive enzyme has been demonstrated. 

 In the first instance the mechanism would appear to be perhaps the initia- 

 tion of an auto-catalytic process. Bodine et al. (1, 3-5) have shown that 

 protyrosinase (a completely inactive form of the enzyme tyrosinase) ob- 

 tained from grasshopper eggs and purified by ammonium sulfate fractiona- 

 tion can be converted into active enzyme by heating at 60°-70°C. The effect 

 of temperature, however, is not unique. Treatment with various detergents, 

 urea, acetone or the simple addition of extracts from grasshopper embryos 

 similarly initiates the activation of the proenzyme. 



In the second instance the activation appears to be related to the de- 

 struction or inactivation by heat of a naturally occurring protein in- 

 hibitor of the enzyme (8, 12). A necessary corollary to this, of course, is 

 that the enzyme in question be relatively heat-stable. In the present paper 

 we shall dwell exclusively on this latter type of heat activation and de- 

 scribe a group of enzymes that are activated by boiling. 



ORIGINAL OBSERVATION 



During the course of studies on the pyridine nucleotide content of Proteus 

 vulgaris X-19 (ATCC 6380), it was noted that whereas trichloracetic acid 

 extracts of this organism contained considerable amounts of these nucleo- 

 tides, aqueous extracts prepared from boiled cells contained primarily 

 nicotinamide riboside (NR) and very little diphosphopyridine nucleotide 

 (DPN) or nicotinamide mononucleotide (NMN). This discrepancy was 

 clarified when subsequent experiments demonstrated the presence, in sonic 

 extracts of this organism, of two enzymes (a DPN pyrophosphatase and a 

 5' nucleotidase) which were essentially inactive unless the extracts were 



^ Contribution No. 152 of the McCollum-Pratt Institute, Johns Hopkins Uni- 

 versity. Aided by grants from the National Science Foundation (Grant No. G 2187), 

 the American Cancer Society as recommended by the Committee on Growth of the 

 National Research Council, and the National Cancer Institute of the National In- 

 stitutes of Health (Grant No. C-2374.C). 



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