STABLE STRUCTUR.\L STATES OF RAT HEART MITOCHONDRIA 



97 



mitochondria. The first is as follows, i . Are there only tzco stable structural 

 states or is it possible to demonstrate a series of intermediate stable states 

 lying betzceen the fully expanded and tJie fully contracted conditions ? 



The second of these alternatives appears to be correct. Rat heart mito- 

 chondria may be brought to a stable expanded configuration by a short 



Fig. 2. Data illustrating {a) the absence of a discernible effect on mitochondrial 

 structure when magnesium chloride is added to a suspension of heart mitochondria 

 which have been brought to a stable expanded condition with phosphate and 

 succinate; and {b) part of a "shrinkage titration" showing the establishment of a 

 series of steadv structural states of mitochondria with increasing concentrations of 

 ADP. 



Extinction changes were recorded and rat heart mitochondria were isolated as 

 described in the legend to Fig. i . Only two of the three simultaneous recordings 

 are shown. Downward deflection of the traces indicates increase of extinction. 

 Horizontal lines have been drawn at intervals of o-oi extinction units. Temperature 

 20•9^ 



9 min. before the beginning of the above record a concentrated suspension of 

 freshly isolated mitochondria was diluted into 0-32 M sucrose, pH 7-4, to give 48 

 ml. of a reaction mixture containing 0-21 mg. biuret protein per ml. Phosphate 

 buffer, pH 7-4 and potassium succinate, pH 7-4 were then added to give final 

 concentrations: phosphate, 5-1 mM ; succinate, 4-1 mM. Extinction changes 

 similar to those shown in Fig. i were then observed, indicating swelling of the 

 mitochondria. A stable expanded condition was finally established and is indicated 

 above by the steady level of the traces at the beginning of the record. \x the point 

 marked Mg the recording was interrupted and 0-5 ml. of 0-09 m magnesium 

 chloride was rapidly stirred into the suspension (final concentration 0-92 mM). 

 The small decrease of extinction which followed was attributable to the effect 

 of dilution. At the points marked ADP 00s ml. of 0-02 M ADP in 0-32 m sucrose 

 was added in the same way. Three further additions of .A.DP were made at 

 intervals immediately following the above record. The optical effects of these later 

 additions are not shown above but are included in Fig. 3 together with the above 

 data. 



