Studies on the electron transport system. XI. Correlation of the morphology and enzymic properties of mitochondrial and sub-mitochondrial particles.

Abstract The morphological changes which mitochondria and their derivative particles undergo during isolation from beef-heart muscle have been studied by electron microscopy. Mitochondria isolated from the tissue in a 0.25 M sucrose medium are grossly modified in structure. By virtue of these modifications they can readily give rise to smaller submitochondrial particles such as ETP and PETP. Morphologically intact mitochondria can be isolated from heart tissue which is comminuted in 0.88 M sucrose but only in relatively small yield. Such mitochondria do not give rise to ETP and PETP by the methods successfully applied to the mitochondria isolated in 0.25 M sucrose. The light mitochondrial fraction contains swollen mitochondria whose outer membrane shows a marked tendency to undergo vesiculation leading to the formation of the electron transport particle. Some or all of the cristae of these swollen mitochondria can be pinched off together with a part of the outer mitochondrial membrane to form new particles which, depending upon size, conform either to the particles of the heavy mitochondrial fraction (large particle) or to PETP (small particle). When the heavy mitochondrial fraction is exposed to sonic irradiation, a smaller particle is liberated which resembles ETP closely both morphologically and chemically. It differs primarily in the respect that bound cytochrome c is readily extractable whereas the bound cytochrome c of ETP is not.