Sedimentation behavior and ultrastructure of mitochondria from repressed and derepressed yeast, <italic>Saccharomyces cerevisiae</italic>

Abstract

1. Yeast (Saccharomyces cerevisiae) was grown under conditions of respiratory repression (10% w/v glucose) and derepression (1% w/v glucose or 2% w/v ethanol), and the cells spheroplasted. 2. Electron photomicrographs of the spheroplasts showed a few large, but otherwise normal-looking mitochondria in repressed cells, and many small mitochondria in the derepressed spheroplasts. 3. Mitochondria from lysates of the spheroplasts were separated by rate-zonal and isopycnic sedimentation in sorbitol gradients in the Z-15 and B-XIV rotors. 4. The mitochondria from repressed cells sedimented rapidly and had mean equilibrium densities of 1.211 gm.cm−3. Mitochondria from fully derepressed cells sedimented one-third as rapidly and had equilibrium densities of 1.194. 5. Spheroplasts of repressed cells when incubated under derepressing conditions showed respiratory derepression. During derepression, a new class of mitochondria appeared with ultrastructural and sedimentation properties similar to those of derepressed cells.