The yeast mitochondrial ATPase complex. Subunit composition and evidence for a latent protease contaminant

Isolation and properties of chloroplast coupling factor from wheat

1. Wheat chloroplast coupling factor (CF1) was extracted with a modification of the chloroform extraction method of Younis et al. (J. Biol. Chem. 252, 1814--1818, 1977). A one-step purification on an 8--25% sucrose gradient yielded a CF1 which was at least 98% pure as judged by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. 2. Inclusion of proteolysis inhibitors during extraction and purification consistently gave a CF1 containing all five subunits. Selective loss of the sigma and epsilon subunits was observed when proteolysis inhibitors were omitted. 3. Proteolysis inhibitors prevented the release of wheat CF1 from the thylakoid by the low-ionic-strength wash method of Strotmann et al. (Biochim. Biophys. Acta, 314, 202--210, 1973). The enzyme extracted with chloroform and low ionic strength were compared by electrophoresis and no evidence of a difference in molecular weight of any subunit was observed. This suggests that a proteolytic event is not required for release of wheat CF1 by the low-ionic-strength method, even though release is inhibited by proteolysis inhibitors. 4. The gamma subunit of wheat CF1 probably contains at least one internal disulfide bridge, as the electrophoretic mobility of this subunit is lower in the presence of reducing agent than in its absence. 5. Wheat CF1 was viewed by the electron microscope after negative staining. Discrete particles, many appearing hexagonal, were observed at high magnifications. Markham rotational analysis confirmed that the enzyme has sixfold symmetry in at least one of its orientations.

Mitochondrially synthesized protein subunits of the yeast mitochondrial adenosine triphosphatase. A reassessment

Evidence is presented that a mitochondrial translation product (Mr, 32,000) previously thought to be a subunit of the membrane sector of the yeast mitochondrial ATPase is a contaminant, consisting of subunit II of the cytochrome oxidase complex and cytochrome b apoprotein. Our data suggest that only two subunits (Mr, 7600 and 20,000) of the mitochondrial ATPase are synthesized in the mitochondria.

Biogenesis of mitochondria. oli2 Mutations affecting the coupling of oxidation to phosphorylation in Saccharomyces cerevisiae

1. Two oligomycin-resistant strains of Saccharomyces cerevisiae have been isolated and shown to have mutations in the oli2 region of the mitochondrial DNA. On solid media containing a non-fermentable energy source, the mutant strains were able to grow only slowly at 28 degrees C and not at all at 18 degrees C or 36 degrees C. 2. When grown in a glucose-limited chemostat at 28 degrees C, the mutant strains were almost completely defective in oxidative metabolism. The mutant mitochondria contained significant levels of all respiratory enzymes, and an active, oligomycin-sensitive ATPase, but the ATP-32Pi exchange activity and P : O ratio were very low. 3. The mutations in these strains are genetically closely linked to mit mutations which have been shown to affect a 20 000-dalton ATPase subunit (Roberts, H., Choo, W.M., Murphy, M., Marzuki, S., Lukins, H.B. and Linnane, A.W. (1979) FEBS Lett. 108, 501-504). Since the mitochondrial ATPase in these mutant strains appears to be fully assembled, the defect in the coupling mechanism is probably a result of a small alteration in the structure of the 20 000-dalton ATPase subunit. 4. When the mutant strains were grown at 18 degrees C, the mitochondria had very low cytochrome oxidase activities, and reduced levels of cytochrome aa3. The largest subunit (Mr 40 000) of this enzyme was not synthesized.

Studies on the structure and conformation of yeast mitochondrial ATPase using aurovertin and methanol as probes

1. The isolation of the mitochondrial ATPase F1 and its beta-subunit from commercial baker's yeast (Saccharomyces cerevisiae) is described. 2. The molecular weight determined by ultracentrifugation is 340000 +/- 30000. Gel chromatography indicates a molecular weight of 300000 +/- 20000. 3. Fluorimetric titration of the isolated enzyme with aurovertin reveals two binding sites per molecule. The isolated beta-subunit binds aurovertin in a 1 : 1 stoicheiometry. It is concluded that the ATPase molecule contains two aurovertin-binding beta-subunits. 4. The stabilizing agent methanol influences both the measured Kd and the concentration of binding sites for aurovertin. These results fit a model in which both F1 and aurovertin are distributed between aqueous and methanol phases. 5. The effect of methanol on the ATPase activity can be described in terms of the model proposed by Recktenwald and Hess (Recktenwald, D. and Hess, B. (1977) FEBS Lett. 76, 25-28). It is proposed that methanol enhances the affinity of the regulatory site for ATP, but at higher concentrations prevents the interaction between the regulatory and catalytic sites. 6. Since HSO(-3), a typical effector of the assumed regulatory site of F1, has no effect on the binding of aurovertin, it is concluded that the binding site of aurovertin is not correlated with the regulatory site. 7. The inhibition of ATPase activity by aurovertin is slowly (t 1/2 = 70 s) induced during turnover conditions. 8. From the effect of methanol on the inhibition of ATPase activity by aurovertin it is concluded that under turnover conditions the conformation is such that the aurovertin-binding sites have a 6-fold higher affinity for methanol than under resting conditions.

Regulation of mitochondrial biogenesis. Occurrence of non-functioning components of the mitochondrial respiratory chain in Saccharomyces cerevisiae grown in the presence of proteinase inhibitors: evidence for proteolytic control over assembly of the respiratory chain

Yeast was grown in glucose- or galactose-containing media without or with proteinase inhibitors, phenylmethanesulphonyl fluoride and pepstatin. Culture growth was practically not affected by these compounds. Yeast growth on glucose in the presence of either phenylmethanesulphonyl fluoride or pepstatin entails accumulation of cytochromes c, c1, b and aa3 to a 25--30% excess above the control by the stationary phase, while cell respiration is unaffected. During growth on galactose the maximal cytochrome content (per unit weight of biomass) is reached in the mid-exponential phase and then decreases by 30--40% towards the stationary phase, while cell respiration remains constant. Addition of phenylmethanesulphonyl fluoride or pepstatin in the mid-exponential phase blocks the decrease in cytochrome levels and has no effect on cell respiration. Mitochondrial populations isolated from stationary-phase control and phenylmethanesulphonyl fluoride-grown cells glucose cultures display identical succinate oxidase and partial-respiratory-chain activities, despite the differences in cytochrome contents. However, the activities of individual respiratory complexes measured after maximal activation are nearly proportional to the amounts of corresponding components. The same situation holds true for mitochondrial populations from mid-exponential-phase, stationary-phase control and stationary-phase inhibitor-grown cells of galactose cultures. The findings suggest that the 'surplus' respiratory-chain components do not participate in electron flow because of the lack of interaction with adjacent carriers.

The role of the light-harvesting chlorophyll a/b protein complex in chloroplast membrane stacking. Cation-induced aggregation of reconstituted proteoliposomes

The major intrinsic protein from spinach chloroplast membranes, the light-harvesting chlorophyll a/b-protein complex, contains two distinct polypeptides of Mr 23,500 and 26,000 and 31% lipid by weight, comprising five diacyl lipids and seven chlorophylls, together with some carotenoids, per 26,000-Mr polypeptide. The chlorophyll a/b ratio is 1.1. Low-temperature fluorescence emission spectra of the light-harvesting complex revealed a major peak at 681 nm with a shoulder of variable intensity at 695 nm. The 695-nm emission has been correlated with a progressive aggregation of the complex into two-dimensional, semi-crystalline sheets. To determine the role of the light-harvesting complex in cation-dependent thylakoid stacking, the purified complex has been quantitatively incorporated into liposomes containing the four major chloroplast diacyl lipids using a simple freeze-thaw technique. The proteoliposomes appeared largely as unilamellar vesicles, with diameters between 0.1 and 0.8 micron. Freeze-fracture analysis showed intramembrane particles of 8-10 nm corresponding to the incorporated complex. Both monovalent and divalent cations caused an immediate aggregation of the proteoliposomes, which was reversed at low cation concentrations and was largely inhibited by prior trypsin treatment. Since lipid vesicles themselves showed none of these effects, it is concluded that surface-exposed polypeptide regions of the light-harvesting complex are directly involved in thylakoid stacking in vivo.