METABOLIC CONTROL OF STRUCTURAL STATES OF MITOCHONDRIA 89 



followed by a strong inhibition. An increase in light-scattering also begins 

 after mannose addition. The respiration and scattering changes are com- 

 pleted at almost the same time. Other hexoses such as 2-deoxyglucose and 

 glucose give similar results. Although scattering changes have been ob- 

 served which are due to tonicity changes of the cells themselves (Lucke 

 and Parpart, [21]), rapidly penetrating carbohydrates such as mannose 

 cause no measurable changes in cell volume as judged by direct determina- 

 tions in control experiments. It was therefore proposed that the changes 

 were of intracellular origin. Similar light-scattering or shrinkage changes 

 are observed by ADP addition to isolated mitochondria from many sources 

 including those of ascites tumour cells. Mitochondrial shrinkage and 

 acceleration of respiration would be the result of the carbohydrate-induced 

 hexokinase reaction which increases the intramitochondrial ADP level. 

 The extensive inhibition of metabolism is believed to result from the un- 

 availability of ATP in the cytoplasmic system. Chance and Hess [20] and 

 Racker [22] imply that the cause is an alteration in the structure of the 

 mitochondrial membrane. In this experiment such a change would seem 

 disclosed by the light-scattering effect. As the production of ADP would 

 be expected to be quite high under the conditions where scattering was 

 increasing, these results may indicate that shrunken mitochondria in 

 vivo can retard the escape of ATP synthesized by oxidative phosphorylation. 



In this regard it is interesting to recall the experiments of Gamble [23] 

 who reported increased retention of bound potassium ions by intact 

 mitochondria under conditions of phosphorylation and, presumably, high 

 shrinkage. Certain structural states of the membrane may favour potassium 

 binding. 



Attempts are being made to design other experiments to test the avail- 

 ability of ATP synthesized by oxidative phosphorylation for extramito- 

 chondrial processes. In one series of experiments Dr. Watanabe and I 

 have made a crude reconstruction of a living muscle fibre [24]. The ATP 

 synthesized by oxidati\e phosphorylation of cardiac muscle mitochondria 

 from ADP and phosphate is made available for the isometric development 

 of tension by a glycerinated muscle fibre. Tension development evoked by 

 ATP alone and by ATP produced by mitochondrial phosphorylation of 

 ADP were compared and the results are recorded in Fig. 4. Respiration 

 of the mitochondrial suspension was traced polarographically and tension 

 development was simultaneously recorded by use of a strain gauge trans- 

 ducer. It was found that tension development runs very closely with 

 oxidative phosphorylation over a range of ADP concentrations varying 

 between 10^^ and lo^^ m. In an experiment in the presence of ADP and 

 mitochondria half-maximum tension was developed when the con- 

 centration of ADP was 2-5 X 10 '^ M (curve A). In the absence of 

 mitochondria with ATP only, half-maximum tension was developed 



