The preparation and some properties of yeast mitochondria

Summary A comparison of the structural and functional integrity of yeast mitochondria prepared by a mechanical disintegration method with that reported for mitochondria prepared by enzyme methods has been made.The mitochondria prepared by mechanical disruption show at least as great a degree of functional integrity as that reported for enzymically prepared mitochondria. This was judged by the substrates oxidised, the rates of these oxidations, the respiratory control and ADP:0 ratios and difference spectra.The respiration of citrate and of ethanol by the mechanically prepared mitochondria has been shown to be stimulated by exogenous NAD; in the case of the latter substrate a degree of respiratory coupling became apparent as a consequence of this stimulation.The penetration of NADH₂, and of citrate or of ethanol in the presence of exogenous NAD, into the mitochondria has been examined.The results are consistent with the reported existence of a NADH₂ dehydrogenase system located in the outer area of the inner mitochondrial membrane. The NAD stimulation of ethanol respiration also suggests the occurrence of an external alcohol dehydrogenase in the mitochondrial preparation; similar results with citrate suggest external forms of aconitic hydratase and isocitric dehydrogenase to be present.Unlike animal mitochondria the rate of penetration of oxidisable substrates in uninhibited suspensions appeared to exceed respiration and/or outward diffusion rates in this preparation.Evidence of a malate stimulated citrate and isocitrate transport system similar to that reported for animal mitochondria is presented, but the specificity of the system for tricarboxylate anion appears to differ, at least in respect of propane 1.2.3 tricarboxylate (tricarbalyllate).