ORGAN THERMOGENESIS 



maximal oxidative activity of this enzyme corresponds to the highest 

 tissue oxygen consumption. It can also be assumed that cytochrome 

 oxidase does not occur in excess quantity in tissues, because cyto- 

 chrome oxidase activity readily becomes adapted to various condi- 

 tions (Tipton and Nixon, 1946; Hannon, 1960). For these reasons the 

 cytochrome oxidase activities of whole animals and their tissues 

 were examined to find whether the values were related to the maxi- 

 mal steady state oxygen consumption. 



The method selected for use in these studies was the classic 

 manometric method of Schneider and Potter (1943), in which cyto- 

 chrome oxidase activity can be measured in terms of oxygen con- 

 sumption. The cytochrome oxidase activity was measured in a homo- 

 genate of the whole animal for direct comparison with the values of 

 maximal steady state metabolism. Before homogenation in distilled 

 water, the animals were depilated and after removal of their diges- 

 tive tract, they were ground in ameatgrinder. Oxygen consumption 

 of the homogenate was measured at 37 C . 



The total cytochrome oxidase activity was determined in seven 

 species of rodents (wood mouse - Apodemus sylvaticus , bank vole - 

 Glethrionomys glareolus, common vole - Microtus arvalis , white 

 mouse, golden hamster, rat, guinea pig) in the range of body weight 

 from 17 to 700 gms. It was found (Figure 5) that the exponent of the 

 relationship between total cytochrome oxidase activity and body 

 weight was very similar to that found for basal and maximal meta- 

 bolism (Jansky, 1961). 



By comparisonof the absolute values of oxygen consumption, ob- 

 tained in vitro, using cytochrome oxidase activity and those in vivo at 

 the level of maximal steady state metabolism, only small differences 

 were found. 



In spite of close agreement between in vivo and in vitro values, 

 they are not considered to be identical. Both methods are completely 

 different, and we cannot expecttobeable to imitate the same condi- 

 tions in vitro as in living cells, where the concentration and com- 

 position of substrates, pH and various other factors can change dur- 

 ing the maximal performance of the organism. In addition there is 

 a possibility that certain organs such as kidney, brain, or gonads are 



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