POIKILOTHERMIC ADAPTATIONS 



PROSSER'. Yes, I think the shifting of the optimum is very 

 important, and this is one of the things that we are proposing to 

 do soon, but I am not sure that I would agree that the cytochrome 

 oxidase system is necessarily the .limiting one for activity meta- 

 bolism since these enzymes seem always present in excess. Are 

 you implying that this is the principal route for activity as opposed 

 to standard metabolism? 



HART: I would not like to say anything about that now, since 

 we will hear more evidence about this later on. 



HANNON: I think at this time we might point out that after 

 one month of acclimatization you do find an increase in cytochrome 

 oxidase activity. I feel that it is important to keep in mind that 

 practically all hydrogen transport from Krebs cycle oxidations 

 eventually channels through this particular enzyme. Thus, it would 

 seem likely that cytochrome oxidase may not be as much in excess 

 as the activity measurements might suggest. In fact, it may even 

 be rate limiting. If this proves true then cytochrome oxidase would 

 be a very good index of maximal metabolic capacity. 



PROSSER: Yes, but we found very little effect on any of the 

 Krebs cycle enzymes that we have looked at. I do not understand 

 the inverse acclimation of some of them. I doubted the phenomenon 

 on the basis of Precht's experiments. However, we came up with 

 two enzymes which show it, and it is highly significant. 



IRVING: One of the things that impressed me is that when we 

 look at the changes of the influences of temperature on various 

 functions we expect to see some more or less continuous slopes, 

 that is, something which will relate the rate to temperature in the 

 form of a curve; and yet many changes of behavior occur explo- 

 sively at given temperatures, whether it be the flight or the biting 

 of the insects, or the sensation of same. Insects do not half fly. 

 They either completely fly or they are completely quiescent. Of 

 course, they also have certain reverse or discontinuous changes — 

 as, for example, in the discharge of cold receptors, which apparently 



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