46 ALBERT L. LEHNINGER 



phosphorus of this fraction has a significantly high rate of turnover [46]. 

 Although preliminary work by Dr. Ishikawa as a test of this possibility 

 appeared very promising, because the mitochondria contain a protein 

 phosphokinase [47], analytical difficulties of an unexpected nature still 

 prevent a clear-cut evaluation. 



However, a rather different development provided an important 

 approach to the chemistry of contraction. This was the finding that 

 mitochondrial swelling induced by reduced glutathione is different from 

 swelling caused by other agents such as phosphate or thyroxine in its 

 kinetics and in its control [48]. Furthermore, swelling induced by gluta- 

 thione is not reversed by ATP under the same conditions which can reverse 

 swelling caused by other agents. It was soon found that this failure of 

 contraction was due to the detachment from the mitochondria of a necessary 



Fig. 7. Requirement of C-factor for contraction of glutathione-swollen 

 mitochondria. 



protein factor (designated C-factor) on exposure to glutathione [49]. This 

 factor leaked out into the medium and could be recovered. Only when this 

 factor was added back in appropriate concentrations to the test medium 

 could contraction of the mitochondria be observed in the presence of 

 ATP + Mg + + + BSxA.. The C-factor can be assayed, as is shown in 

 Fig. 7, by the level of contraction achieved as a function of the concentra- 

 tion of the factor in the medium. With this simple bioassay it was found 

 possible to demonstrate the occurrence of C-factor in sonic extracts of 

 mitochondria and in extracts of digitonin particles. It was found not be to 

 dialyzable, it is labile to heat, and survives acetone drying or lyophilization. 

 It has now been purified over fifty-fold by Dr. Diether Neubert. 



Recently we have carried out an examination of C-factor activity in 

 different tissues and in different tissue fractions [50] with the surprising 

 finding that this factor is found not only in mitochondria but also in extra- 

 mitochondrial cytoplasm. C-factor activity has been found in the mito- 

 chondria and extra-mitochondrial cytoplasm of a number of tissues of the 



