COMPONENTS OF THE ENERGY-COUPLING MECHANISM 



39 



This activity, called M-factor, can be assayed semi-quantitatively with 

 the system shown and it has been purified over fortyfold. The starting 

 material is either a phosphate extract of acetone-powdered mitochondria, 

 from which M-factor can be precipitated by relatively low concentrations 

 of ammonium sulphate or, curiously, simple extracts of whole fresh rat 

 liver mitochondria made with 0-3 M ammonium sulphate. Al-factor 

 activitv from such extracts can then be recovered by further treatment 

 with ammonium sulphate. The M-factor preparations contain essentially 

 no ATP-ase activitv, ATP-P/'^- exchange activity or ATP-ADP exchange 

 acti\itv. Thev are also free of adenylate kinase and protein phosphokinase. 



100 



DNP-SENSITIVE PORTION 



5^q. lO^g 20;ig 



M-FACTOR 



Fig. 4. Increase of DXP-sensitivity of .\TP-ADP exchange in digitonin 

 particles by Al-factor. 



Two possibilities are open for the mechanism of action of M-factor. 

 The first is that M-factor is a specific "cementing" protein capable of 

 binding with the ATP~ADP exchange enzyme molecule in such a manner 

 as to hold it in the appropriate geometry on the digitonin particle so that 

 it may become reactive with the preceding, DPX-sensitive reaction. On 

 the other hand, Al-factor may itself be an intermediate enzyme of the 

 energy-coupling mechanism. A possible mode of action is given in the 

 following equations: 



electron 



Carrier-'^M 



Carrier + P'^ 

 P-^E + M 

 ATP + E 



A I 



(7) 



(S) 



in which E represents the ATP-ADP exchange enzyme and Carrier-^-M 

 the high-energv complex of the carrier generated during electron transfer. 

 M thus could be visualized as replacing the X of the earlier formulation 



