98 F. A. HOLTON AND D. D. TYLER 



incubation with phosphate and succinate (Fig. i). Addition of magnesium 

 chloride does not alter this configuration (Fig. 2), but it activates a power- 

 ful ATPase [5] which can hydrolyze newly synthesized ATP at least as 



► 002 



+ 001 



50 100 150 



External ADP concentration 

 /i. Molar 



Fig. 3. Relationship between the concentration of externally added ADP and 

 the resultant extinction changes measured simultaneously at three separate wave- 

 lengths in a suspension of heart mitochondria in the presence of magnesium ions. 

 Data of Fig. 2 graphed, with addition of results relating to later additions of ADP 

 and also from simultaneous observations at 434 m/x. 



The changes of extinction caused by ADP clearly did not obey Rayleigh's law, 

 since for any given concentration of ADP they did not decrease regularly with 

 increasing wavelength of observation. The data suggests that a minor part of the 

 extinction changes observed was due to an alteration in the extinction due to pig- 

 ments as ADP was added. They are consistent with the hypothesis that the states 

 of oxidation of both cytochrome b and flavoprotein were moved in the direction of 

 oxidation by addition of ADP, an eifect to be expected from the work of Chance and 

 Baltscheffsky [12]. If it is assumed that there was no contribution of pigments to 

 the extinction changes recorded at 450 m/x, it is possible to calculate for the other 

 two wavelengths of observation values of the ratio 



extinction change due to light scattering 

 extinction change due to pigment 

 For observations at both 434 m^i and 477 ■ 5 m/Lt the above data give a value of 

 3 -4 for the above ratio. This value may be compared with that from the work of 

 Chance and Packer [13], who added ADP to a suspension of rat heart sarcosomes 

 and deduced a value of about 4 for the same ratio. (In their work the extinction 

 change due to scattering was equated to that observed at 443 m/x and the extinction 

 change due to pigment was equated to the difference between the changes observed 

 at 430 m/t and at 443 m/i.) 



fast as the respiratory chain, oxidizing succinate, can produce it. Under 

 these conditions added ADP is maintained at the concentration at which 

 it has been added while the processes of oxidative phosphorylation con- 

 tinue normally. Figures 2 and 3 illustrate the optical effects of successive 



