Calcium Uptake by Potato Tuber Mitochondria

An attempt was made to isolate from potato tuber mitochondria the reported calcium-45 complex. Mitochondria fractionation results showed that the lipids were not involved in the calcium-45 complex formation. Using hot water as an extracting solvent it was found that two calcium-45 complexes occurred in the mitochondria fraction. One of the complexes was readily removable while the other complex was much less readily extractable with hot water. The readily removable calcinm-45 complex was identified as calcium phosphate and the less readily extractable complex seemed to be directly related to mitochondrial RNA liberation, however, it was impossible to isolate a calcium-45 ribonucleic acid complex. The extraction of the slowly removable calcium-45 complex was not a simple liberation of the complex but rather a breakdown which was irreversible and could be inhibited partially by sodium arsenate. A possible explanation of these data is that the TCA soluble fraction represents the total calcium45 uptake by the mitochondria, that is, the calcium-45 that has been accumulated plus that which is in the “calcium-carrier complex”. It is suggested that the easily extractable hot water fraction is the accumulated calicum-45 while the less readily extractable fraction is the “calcium-carrier complex”.