PROSSER 



HANNON; This may or may not be true; I do not feel that we 

 have enough evidence at the present time to justify any firm con- 

 clusions either way. One basic difference between these two t3T)es of 

 animals that should be noted, however, is the decline in the meta- 

 bolic rate of the poikilotherm when he is exposed to high ambient 

 temperatures. This is quite in contrast to the response of the homeo- 

 therm, in which exposure to high ambient temperatures has either 

 no effect on or increases the metabolic rate. 



This high temperature decline in the metabolic rate in fish and 

 other poikilotherms is most interesting to me from the standpoint 

 of its similarity to the effect of temperature on many enzymes. 

 There are a great many enzymes that show increasing activities 

 with increasing temperature until some critical point, or tempera- 

 ture optimum, is reached. Beyond this temperature optimum the 

 activity declines. In many enzymes this decline at high temperatures 

 is reversible, provided the point of protein denaturation is not 

 reached. 1 would imagine that a similar reversible inactivation 

 would also apply to the overall respiratory metabolism of poikilo- 

 therms. 



PROSSER; Yes, but I do not think that the same thing is hap- 

 pening here. This is a result of acclimation. The direct metabolism 

 temperature effect is what one finds in short term exposure to the 

 heat. The acclimatory reduction in metabolism at high temperature 

 takes days to develop, just as does the increase in metabolism in 

 cold. 



HANNON: To the best of my knowledge, instead of reducing 

 metabolism at high temperatures, as the poikilotherms do, the 

 mammals increase their heat loss. Thislfeelis a basic difference. 



At the cellular and sub-cellular level, I was quite impressed 

 by the many striking similarities between the metabolic activities 

 of poikilotherms and homeotherms following cold-acclimatization. 

 In fact, I do not feel there are as many incongruities here as you 

 do. For instance, you have given a number of examples where cold 

 acclimatization leads to an increase in the metabolic rate of the 

 intact animal. You have also shown with whole cell preparations 



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