Turnover of mitochondrial inner membrane proteins in hepatoma monolayer cultures

The degradation rates of inner mitochondrial membrane proteins were examined in serum-deprived hepatoma cultures. In those nonproliferating cells, the degradation of composite mitochondrial proteins was a first order process with a half-life of 34 h. The half-lives of specific inner mitochondrial membrane polypeptides were determined by examining the 3H/35S of isolated polypeptides from cells given [3H]methionine and [35S]methionine pulses, respectively, before and after a 2-day chase period. The 33 most abundant polypeptides resolved on a bidirectional polyacrylamide gel system showed half-lives ranging from 20 to 100+ h. The 15 polypeptides translated on mitochondrial ribosomes in the presence of inhibitory concentrations of cycloheximide also displayed heterogeneous rates of degradation (t1/2 = 35-100+ h). None of the isolated adenosine triphosphatase (coupling factor F1) or immunoprecipitated cytochrome c oxidase subunits were significantly turned over during the case period. Five of eight cytochrome b-c1 complex subunits, however, were turned over significantly more rapidly (t1/2 = 39-42 h) than the other three (t1/2 = 94+ h). The results demonstrate heterogeneous degradation rates for inner membrane polypeptides, extending in some cases to those within the same respiratory complex.     

Properties of the F0F1 ATPase complex from Rhodospirillum rubrum chromatophores, solubilized by Triton X-100.

1. A cold-stable oligomycin-sensitive F0F1 ATPase complex from chromatophores of Rhodospirillum rubrum FR 1 was solubilized by Triton X-100 and purified by gel filtration. 2. The F0F1 complex is resolved by sodium dodecyl sulfate electrophoresis into 14 polypeptides with approximate molecular weights in the range of 58000--6800; five of these polypeptides are derived from the F1 moiety of the complex which carries the catalytic centers of the enzyme. 3. The purified F0F1 complex is homogeneous according to analytical ultracentrifugation and isoelectric focusing. 4. The molecular weight as determined by gel filtration is about 480 000 +/- 30 000. S020,w is 1.45 +/- 0.1 S and the pI is 5.4. 5. The amino acid composition of the F0F1 complex is compared with the data obtained for the F1 moiety of the enzyme. 6. Quantitative data on the sensitivity to N,N'-dicyclohexyl-carbodiimide as well as kinetic parameters, regarding substrate specificity and dependence of ATPase activity on divalent cations, are reported.     

The definition of mitochondrial H+ ATPase assembly defects in mit- mutants of Saccharomyces cerevisiae with a monoclonal antibody to the enzyme complex as an assembly probe

mit- mutants with genetically defined mutations in the mitochondrial structural genes of the H+-ATPase membrane subunits 6, 8 and 9 were analysed to determine the H+-ATPase assembly defects that resulted as a consequence of the mutations. These include mutants which do not synthesize one of the membrane subunits and mutants which can synthesize these subunits, but in an altered form. Protein subunits which can still be assembled to the defective H+-ATPase in these mutants were determined by immunoprecipitation using a monoclonal antibody to the beta-subunit of the enzyme complex. The results suggest that the assembly pathway of the mitochondrially synthesized H+-ATPase subunits involves the sequential addition of subunits 9, 8 and 6 to a membrane-bound F1-sector. In addition to subunits of the F0- and F1-sectors, two other polypeptides (Mr = 18,000 and Mr = 25,000) are associated with the yeast H+-ATPase. These polypeptides were not observed in the immunoprecipitates obtained from mutants in which the F0-sector is not properly assembled.     

Energy-linked reactions catalyzed by the purified ATPase complex (F0F1) from Rhodospirillum rubrum chromatophores

1. The isolation of F0F1-ATPase complex from Rhodospirillum rubrum chromatophores by the use of taurodeoxycholate is described. 2. The enzyme preparation contains about 12 polypeptides; five are subunits of the F1 moiety. 3. The ATPase activity of the purified enzyme is dependent on the addition of phospholipids. 4. Km-vales for Mg2+-ATP and Ca2+-ATP are similar to the values obtained for the membrane-bound enzyme. 5. The F0F1-ATPase complex is more than 70% inhibited by oligomycin and N,N'-dicyclohexylcarbodiimide. 6. The F0F1-ATPase complex was integrated into liposomes. The reconstituted proteoliposomes catalyzed energy transduction as shown by ATP-dependent quenching of acridine dye fluorescence and ATP-32Pi exchange.     

Identification of the subunits of F1F0-ATPase from bovine heart mitochondria.

An oligomycin-sensitive F1F0-ATPase isolated from bovine heart mitochondria has been reconstituted into phospholipid vesicles and pumps protons. this preparation of F1F0-ATPase contains 14 different polypeptides that are resolved by polyacrylamide gel electrophoresis under denaturing conditions, and so it is more complex than bacterial and chloroplast enzymes, which have eight or nine different subunits. The 14 bovine subunits have been characterized by protein sequence analysis. They have been fractionated on polyacrylamide gels and transferred to poly(vinylidene difluoride) membranes, and N-terminal sequences have been determined in nine of them. By comparison with known sequences, eight of these have been identified as subunits beta, gamma, delta, and epsilon, which together with the alpha subunit form the F1 domain, as the b and c (or DCCD-reactive) subunits, both components of the membrane sector of the enzyme, and as the oligomycin sensitivity conferral protein (OSCP) and factor 6 (F6), both of which are required for attachment of F1 to the membrane sector. The sequence of the ninth, named subunit e, has been determined and is not related to any reported protein sequence. The N-terminal sequence of a tenth subunit, the membrane component A6L, could be determined after a mild acid treatment to remove an alpha-N-formyl group. Similar experiments with another membrane component, the a or ATPase-6 subunit, caused the protein to degrade, but the protein has been isolated from the enzyme complex and its position on gels has been unambiguously assigned. No N-terminal sequence could be derived from three other proteins. The largest of these is the alpha subunit, which previously has been shown to have pyrrolidonecarboxylic acid at the N terminus of the majority of its chains. The other two have been isolated from the enzyme complex; one of them is the membrane-associated protein, subunit d, which has an alpha-N-acetyl group, and the second, surprisingly, is the ATPase inhibitor protein. When it is isolated directly from mitochondrial membranes, the inhibitor protein has a frayed N terminus, with chains starting at residues 1, 2, and 3, but when it is isolated from the purified enzyme complex, its chains are not frayed and the N terminus is modified. Previously, the sequences at the N terminals of the alpha, beta, and delta subunits isolated from F1-ATPase had been shown to be frayed also, but in the F1F0 complex they each have unique N-terminal sequences.(ABSTRACT TRUNCATED AT 400 WORDS)     

Conformational states of the (Na+ + K+)-transporting ATPase. Formation of 240 000-Mr and 116 000-Mr polypeptides in the presence of a bifunctional thiol probe.

Interpeptide cross-linking of alpha-subunits with concomitant loss of Na+ + K+-transporting ATPase (Na+, K+-ATPase) activity was found when the purified lamb kidney enzyme was treated with the bifunctional thiol reagent 4,4'-difluoro-3,3'-dinitrodiphenyl sulphone (F2DNS). Several forms of the enzyme could be clearly distinguished: one binding ATP (non-phosphorylated enzyme, E1 X ATP), a phosphorylated form (E2-P) and a phosphoenzyme-ouabain complex (E2P X ouabain). A polypeptide of approx. Mr 240 000 and probable alpha 2 composition comprised up to 5-20% of the total polypeptides after reaction of the lamb kidney Na+, K+-ATPase with F2DNS. The amount of this polypeptide formed was related to the conformational state of the enzyme. The presence of adenine nucleotide greatly diminished the amount of 240 000-Mr polypeptide formed and provides evidence for an enzyme-adenine-nucleotide complex under conditions where the enzyme is not phosphorylated. F2DNS reacted with the enzyme in the presence of Mg2+, Pi and ouabain to form a new polypeptide with an approx. Mr of 116 000, and comprised 23% of the total, whereas the 240 000-Mr polypeptide comprised 9% of the total. This suggests that the 116 000-Mr polypeptide is a characteristic marker of the E2P X ouabain complex. By using specific antibodies it was established that both the 240 000- and 116 000-Mr polypeptides contained alpha-, but not beta-, subunits of the Na+, K+-ATPase.     

Immunochemical studies on the large polypeptide of electrophorus electroplax (Na+ + K+)-ATPase.

Antibodies against Lubrol-solubilized Electrophorus electroplax (Na+ + K+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) and its 96 000-dalton polypeptide (P96) were raised in rabbits. The P96 antibody does not cross react with the (Na+ + K+)-ATPase from mammalian species and tissues, but it cross reacts with the (Na+ + K+)-ATPase from both Electrophorus electroplax and brain. The combination of enzyme with anti-P96 is found to inhibit phosphoryl enzyme formation to the same extent that it inhibits enzyme activity. The rate of K+-sensitive dephosphorylation of phosphoryl enzyme appears to be unchanged. These are also found to be true with the antibody against the whole enzyme. Upon tryptic digestion of the enzyme-anti-P96 complex only the large polypeptide of the enzyme is protected. In the case of enzyme-anti-Lubrol-solubilized enzyme complex, both the large and small polypeptides are protected, whereas preimmune sera are without any protecting effect. The data indicate that the phosphoryl acceptor polypeptide and the Lubrol-solubilized electroplax (Na+ + K+)-ATPase from which the polypeptide is derived are phylogenetically distinct from those of the mammalian (Na+ + K+)-ATPases. The selective tryptic resistance of the enzyme-anti-P96 complex indicates that the two polypeptides are spatially well separated, possibly on opposite sides of the membrane.     

The 55-kDa polypeptide released from spinach thylakoid membranes with 1 M LiCl is not the beta subunit of chloroplast F1

It was reported by Frasch et al. (Frasch, W. D., Green, J., Caguiat, J., and Mejia, A. (1989) J. Biol. Chem. 264, 5064-5069) that washing spinach thylakoid membranes with 1 M LiCl caused the release of the beta subunit of chloroplast F1 (CF1) which, existing as 180-kDa complexes of beta 3, retained considerable ATPase activity. We repeated their procedures and confirmed that a CF1 beta-like 55-kDa polypeptide was a major constituent of the 1 M LiCl-washed extract. However, the extract contained another polypeptide of which the Mr was 14,000, and these two polypeptides comprised a complex with approximate Mr 550,000 that had the same mobility in native polyacrylamide gel electrophoresis as that of ribulose-1,5-bisphosphate carboxylase. Only very low ATPase activity, less than 1% of the reported value, was detected for the extract and the purified complex. Antibody against the beta subunit of F1 from a thermophilic bacterium PS3 showed a clear cross-reactivity with the CF1 beta subunit but not with the 55-kDa polypeptide. Analysis of the N-terminal amino acid sequences of the 55- and 14-kDa polypeptides and the whole complex revealed that the complex was ribulose-1,5-bisphosphate carboxylase and that the 55- and 14-kDa polypeptides were its large and small subunits, respectively.     

Purification of measles virus and characterization of subviral components.

Purified measles virus was obtained from [35S]methionine-labeled cells infected at 33 degrees C and maintained in the absence of fetal calf serum. The pellet that was produced by a single high-speed ultracentrifuge spin of culture medium contained virus of purity sufficient for structural analysis. Purified virions contain seven polypeptides with estimated molecular weights of: L, 200,000; G, 80,000; P2, 70,000; NP, 60,000; A, 43,000; F1, 41,000; and M, 37,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Treatment of virions with 0.25% trypsin resulted in a less dense particle which lacked polypeptides G and F1. Solubilization of the viral membrane with the detergent Triton X-100 in low-salt buffer resulted in the loss of the G polypeptide, whereas in the presence of 1 M KCl, Triton X-100 also removed most of the M polypeptide. The nucleocapsids (p = 1.3) obtained from virions treated with Triton X-100 and 1 M KCl contained the L, P2, NP, and M polypeptides. Nucleocapsids isolated from the cytoplasm of infected cells were predominantly composed of the NP polypeptide with smaller amounts of either polypeptide P2 or novel polypeptides, related to NP, with estimated molecular weights of 56,000 to 58,000 and 45,000 to 46,000. A significant amount of polypeptide L was always found in association with nucleocapsids isolated either from virions or from the cytoplasm of infected cells. A membrane component containing the viral membrane polypeptides G, F1, and M was also isolated from infected cells. The data presented here thus suggest that L is an integral part of the nucleocapsid complex. In addition, 37,000-molecular-weight polypeptide (M) appears to have the function described for the matrix proteins of other paramyxoviruses.     

Purification and characterization of the F1-ATPase from Clostridium thermoaceticum.

The F1 portion of the H+-ATPase from Clostridium thermoaceticum was purified to homogeneity by solubilization at low ionic strength, ion-exchange chromatography, and gel filtration. The last indicated the Mr to be 370,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the pure enzyme revealed four bands with Mr corresponding to 60,000, 55,000, 37,000, and 17,000 in an apparent molar ratio of 3:3:1:1. The purified enzyme would bind to stripped membranes to reconstitute dicyclohexylcarbodiimide-sensitive ATPase activity. Phosphohydrolase activity, measured at 58 degrees C, was optimal at pH 8.5. In the presence of a 1 mM excess of Mg2+ over the concentration of ATP, the Km for ATP was 0.4 mM, and the Vmax was 6.7 mumol min-1 mg-1. Unlike the membrane-bound F1F0 complex, the F1-ATPase was relatively insensitive to the inhibitors dicyclohexylcarbodiimide and tributyltin chloride. Both the complex and the F1-ATPase were inhibited by quercetin, azide, 7-chloro-4-nitro-benz-2-oxa-1,3-diazole, and free magnesium, and both were stimulated by primary alcohols and sulfite. In whole cells, the F1F0-ATPase catalyzed the synthesis of ATP in response to a pH gradient.     

Streptococcal cytoplasmic pH is regulated by changes in amount and activity of a proton-translocating ATPase

The Streptococcus faecalis H+-ATPase (F1 X F0 complex) level was elevated when the cytoplasmic pH was shifted below 7.5. The elevated level was attained by the increase in functional unit (F1 X F0 complex) in membranes, but not by the activation of the enzyme. Our data strongly suggested that the increase in enzyme arises from stimulation of enzyme biosynthesis. When calls growing at pH 7.6 were transferred to an acid medium with a pH below 7, the amount of H+-ATPase increased. The amount of H+-ATPase decreased to the basal level when the medium was alkalized again. Cytoplasmic pH was not controlled normally in cells where a change in the amount of H+-ATPase was inhibited. Based on these findings and previous data (Kobayashi, H. (1985) J. Biol. Chem. 260, 72-76), we propose a model for the regulatory mechanism of streptococcal cytoplasmic pH: the pH is regulated by changes in amount and activity of the H+-ATPase, which are dependent on the cytoplasmic pH.     

Cleavage of type 2 adenovirus DNA BY HaeIII endonuclease. II. Map of HaeIII sites in EcoRI fragments C and E

1. A new method for the isolation of the oliogomycin-sensitive ATPase from beef-heart mitochondria is described. 2. A Triton-soluble ATPase complex was isolated as a by-product of the standard procedure, or as the main product when the submitochondrial particles were pretreated with 1% Triton. The ATPase activity of this complex is sensitive neither to oligomycin nor to dicyclohexylcarbodiimide. 3. The ATPase activity of the oligomycin-sensitive ATPase complex is nearly completely dependent on added phospholipids. The highest activation was found with asolectin. 4. The oligomycin-sensitive complex can be integrated into phospholipid vesicles resulting in an ATP- and Mg2+-dependent energization of the vesicles as monitored with the fluorescent dye 9-amino-6-chloro-2-methoxyacridine. 5. Aurovertin-binding studies based on fluorescence measurement reveal the presence of 1.5 mumol aurovertin-binding sites per g protein for the oligomycin-sensitive complex and about 2.2 mumol for the oligomycin-insensitive complex. 6. The preparation of the oligomycin-sensitive complex contains at least 6--7 polypeptides in addition to those derived from F1. One of these polypeptides, with an apparent molecular weight of 31 000, is virtually absent from the oligomycin-insensitive complex. 7. Some of these polypeptides have been identified and isolated.     

Antibodies to the photosystem I chlorophyll a + b antenna cross-react with polypeptides of CP29 and LHCII

A chlorophyll (a + b)--protein complex associated with photosystem I (PSI) was isolated from a larger PSI complex (CPIa) produced by electrophoresis of barley thylakoids solubilized with 300 mM octyl glucoside. It had an apparent Mr of 35,000-43,000 on 7.5% and 10% acrylamide gels respectively, and a chlorophyll a/b ratio of 2.5 +/- 1.5. Denaturation released four polypeptides migrating between 21-24 kDa. They were well separated from the polypeptides of the two photosystem II chlorophyll a + b antenna complexes: LHCII (25-27 kDa) and CP29 (28-29 kDa). In order to study the PSI antenna complex, antibodies were raised against highly purified CPIa. The antigen appeared to be pure when electrophoresed, blotted and reacted with its antiserum, i.e. anti-CPIa detected only the 64-66-kDa CPI apoprotein and the four 21-24 kDa antenna polypeptides. However, when blotted against the whole spectrum of thylakoid proteins, it cross-reacted with both LHCII and CP29 apoproteins. Removal of anti-CPI activity from the anti-CPIa did not affect these cross-reactions, showing that they were not due to antibodies directed against CPI. To show that the same antibody population was reacting with both the photosystem I and photosystem II antenna polypeptides, anti-CPIa was adsorbed onto highly purified CPIa on nitrocellulose. The bound antibody was eluted and used again in a Western blot against whole thylakoid proteins. This selected antibody population showed the same relative strength of reaction with photosystem I and photosystem II antenna polypeptides as the original antibody population had. Similar observations have been made with antibodies to the two photosystem II antenna complexes. We therefore conclude that there are antigenic determinants in common among the chlorophyll a + b binding polypeptides, and predict that there could be amino acid sequence similarities.     

Purification and properties of H+-translocating, Mg2+-adenosine triphosphatase from vacuolar membranes of Saccharomyces cerevisiae

H+-translocating, Mg2+-ATPase was solubilized from vacuolar membranes of Saccharomyces cerevisiae with the zwitterionic detergent N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate and purified by glycerol density gradient centrifugation. Partially purified vacuolar membrane H+-ATPase, which had a specific activity of 18 units/mg of protein, was separated almost completely from acid phosphatase and alkaline phosphatase. The purified enzyme required phospholipids for maximal activity and hydrolyzed ATP, GTP, UTP, and CTP, with this order of preference. Its Km value for Mg2+-ATP was determined to be 0.21 mM and its optimal pH was 6.9. ADP inhibited the enzyme activity competitively, with a Ki value of 0.31 mM. The activity of purified ATPase was strongly inhibited by N,N'-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, tributyltin, 7-chloro-4-nitrobenzoxazole, diethylstilbestrol, and quercetin, but was not affected by oligomycin, sodium azide, sodium vanadate, or miconazole. It was not inhibited at all by antiserum against mitochondrial F1-ATPase or mitochondrial F1-ATPase inhibitor protein. These results indicated that vacuolar membrane H+-ATPase is different from either yeast plasma membrane H+-ATPase or mitochondrial F1-ATPase. The vacuolar membrane H+-ATPase was found to be composed of two major polypeptides a and b of Mr = 89,000 and 64,000, respectively, and a N,N'-dicyclohexylcarbodiimide binding polypeptide c of Mr = 19,500, whose polypeptide composition was also different from those of either plasma membrane H+-ATPase or mitochondrial F1-ATPase of S. cerevisiae.     

Biochemical characterization of the yeast vacuolar H(+)-ATPase

The yeast vacuolar proton-translocating ATPase was isolated by two different methods. A previously reported purification of the enzyme (Uchida, E., Ohsumi, Y., and Anraku, Y. (1985) J. Biol. Chem. 260, 1090-1095) was repeated. This procedure consisted of isolation of vacuoles, solubilization with the zwitterionic detergent ZW3-14, and glycerol gradient centrifugation of the solubilized vacuoles. The fraction with the highest specific activity (11 mumol of ATP hydrolyzed mg-1 min-1) included eight polypeptides of apparent molecular masses of 100, 69, 60, 42, 36, 32, 27, and 17 kDa, suggesting that the enzyme may be more complex than the three-subunit composition proposed from the original purification. The 69-kDa polypeptide was recognized by antisera against the catalytic subunits of two other vacuolar ATPases and labeled with the ATP analog 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, indicating that it contains all or part of the catalytic site. A monoclonal antibody was prepared against this subunit. Under nondenaturing conditions, the antibody immunoprecipitated eight polypeptides, of the same molecular masses as those seen in the glycerol gradient fraction, from solubilized vacuolar vesicles. All eight of these polypeptides are therefore good candidates for being genuine subunits of the enzyme. The structure and function of the yeast vacuolar H+-ATPase were further characterized by examining the inhibition of ATPase activity by KNO3. In the presence of 5 mM MgATP, 100 mM KNO3 inhibited 71% of the ATPase activity of vacuolar vesicles, and the 69- and 60-kDa subunits (and possibly the 42-kDa subunit) were removed from the vacuolar membrane to a similar extent. At concentrations of less than 200 mM KNO3, the stripping of the ATPase subunits and the inhibition of ATPase activity were dependent on the presence of MgATP, suggesting that this is a conformation-specific disassembly of the enzyme. The yeast vacuolar H+-ATPase is a multisubunit enzyme, consisting of a combination of peripheral and integral membrane subunits. Its structure and subunit composition are very similar to other vacuolar ATPase, and it shares some characteristics with the F1F0-ATPases.     

Enhanced synthesis and secretion of type IV collagen and entactin during adipose conversion of 3T3-L1 cells and production of unorthodox laminin complex

Synthesis and secretion of basement membrane proteins by 3T3-L1 adipocytes were studied by metabolic labeling of the cells with [35S]methionine. Enhanced synthesis and secretion of many polypeptides of high molecular weight were observed by stimulating the adipose conversion of 3T3-L1 fibroblasts with dexamethasone, 1-methyl-3-isobutylxanthine, and insulin. Among these polypeptides, alpha 1(IV) and alpha 2(IV) chains of collagen were identified based on specific immunoprecipitation and digestion with bacterial collagenase. Synthesis and secretion of alpha 1(IV) and alpha 2(IV) chains were negligible in the fibroblasts, but remarkably enhanced in adipocytes. Based on specific immunoprecipitation of a sulfated polypeptide of 150 kDa, enhanced (6-fold) synthesis and secretion of entactin were also demonstrated. Immunoprecipitation with anti-laminin antiserum showed synthesis of three polypeptides with sizes corresponding to B subunits but failed to demonstrate synthesis of the A subunit. Synthesis of these laminin-related polypeptides remained constant during the conversion. Nonreducing sodium dodecyl sulfate electrophoresis showed intracellular assembly of three laminin-related polypeptides into binary and ternary complexes in a similar sequence of AB1B2 formation via B1B2 in embryonal carcinoma F9 (Morita, A., Sugimoto, E., and Kitagawa, Y. (1985) Biochem. J. 229, 259-264). The ternary complex of laminin in 3T3-L1 cells had a size significantly smaller than AB1B2 complex in F9 cells. In this complex, a novel subunit appears to take the place of the A subunit. Thus, a novel laminin complex is produced by 3T3-L1 cells.     

Valyl-tRNA synthetase from rabbit liver. I. Purification as a heterotypic complex in association with elongation factor 1

Valyl-tRNA synthetase occurs as a high molecular mass entity of approximately equal to 700 kDa in the crude extract from rabbit liver. The enzyme was purified as a heterotypic complex comprising four polypeptides of 140, 50, 35, and 27 kDa in the molar proportions of 1:2:1:1, respectively, as determined by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Co-purification of these components at each step of the purification supports the conclusion that they are physically associated within the same complex. In addition to valyl-tRNA synthetase activity, which was assigned to the 140-kDa component, the purified complex exhibits a potent Elongation Factor 1 activity, determined by its ability to sustain poly(U)-dependent polyphenylalanine synthesis in the presence of Elongation Factor 2. Our results are essentially in agreement with those from a recent report (Motorin, Y., Wolfson, A., Orlovsky, A., and Gladilin, K. (1988) FEBS Lett. 238, 262-264), according to which the polypeptides other than that assigned to valyl-tRNA synthetase correspond to the subunits of Elongation Factor 1H.     

Plant mitochondrial F0F1 ATP synthase. Identification of the individual subunits and properties of the purified spinach leaf mitochondrial ATP synthase.

Spinach leaf mitochondrial F0F1 ATPase has been purified and is shown to consist of twelve polypeptides. Five of the polypeptides constitute the F1 part of the enzyme. The remaining polypeptides, with molecular masses of 28 kDa, 23 kDa, 18.5 kDa, 15 kDa, 10.5 kDa, 9.5 kDa and 8.5 kDa, belong to the F0 part of the enzyme. This is the first report concerning identification of the subunits of the plant mitochondrial F0. The identification of the components is achieved on the basis of the N-terminal amino acid sequence analysis and Western blot technique using monospecific antibodies against proteins characterized in other sources. The 28-kDa protein crossreacts with antibodies against the subunit of bovine heart ATPase with N-terminal Pro-Val-Pro- which corresponds to subunit F0b of Escherichia coli F0F1. Sequence analysis of the N-terminal 32 amino acids of the 23-kDa protein reveals that this protein is similar to mammalian oligomycin-sensitivity-conferring protein and corresponds to the F1 delta subunit of the chloroplast and E. coli ATPases. The 18.5-kDa protein crossreacts with antibodies against subunit 6 of the beef heart F0 and its N-terminal sequence of 14 amino acids shows a high degree of sequence similarity to the conserved regions at N-terminus of the ATPase subunits 6 from different sources. ATPase subunit 6 corresponds to subunit F0a of the E. coli enzyme. The 15-kDa protein and the 10.5-kDa protein crossreact with antibodies against F6 and the endogenous ATPase inhibitor protein of beef heart F0F1-ATPase, respectively. The 9.5-kDa protein is an N,N'-dicyclohexylcarbodiimide-binding protein corresponding to subunit F0c of the E. coli enzyme. The 8.5-kDa protein is of unknown identity. The isolated spinach mitochondrial F0F1 ATPase catalyzes oligomycin-sensitive ATPase activity of 3.5 mumol.mg-1.min-1. The enzyme catalyzes also hydrolysis of GTP (7.5 mumol.mg-1.min-1) and ITP (4.4 mumol.mg-1.min-1). Hydrolysis of ATP was stimulated fivefold in the presence of amphiphilic detergents, however the hydrolysis of other nucleotides could not be stimulated by these agents. These results show that the plant mitochondrial F0F1 ATPase complex differs in composition from the other mitochondrial, chloroplast and bacterial ATPases. The enzyme is, however, more closely related to the yeast mitochondrial ATPase and to the animal mitochondrial ATPase than to the chloroplast enzyme. The plant mitochondrial enzyme, however, exhibits catalytic properties which are characteristic for the chloroplast enzyme.     

F0F1-ATPase of plant mitochondria: isolation and polypeptide composition

A simple and high yield purification procedure for the isolation of F0F1-ATPase from spinach leaf mitochondria has been developed. This is the first report concerning purification and composition of the plant mitochondrial F0F1-ATPase. The enzyme is selectively extracted from inner membrane vesicles with the zwitterionic detergent, 3-[(3-cholamidopropyl) dimethyl ammonio]-1- propane sulfonate (CHAPS). The purified enzyme exhibits a high oligomycin-sensitive ATPase activity (3,6 mumol.min-1.mg-1). SDS-PAGE of the purified F0F1-ATPase complex reveals protein bands of molecular masses of 54 kDa (F1 alpha,beta), 33 kDa (F1 gamma), 28 kDa, 23 kDa, 21 kDa (F1 delta), 18.5 kDa, 15 kDa, 10.5 kDa, 9.5 kDa (F1 epsilon) and 8.5 kDa. All polypeptides migrate as one complex in a polyacrylamide gradient gel under non-denaturing conditions in the presence of 0.1% Triton X-100. Five polypeptides could be identified as subunits of F1. Polypeptides of molecular masses 28 kDa, 23 kDa, 18.5 kDa, 15 kDa, 10.5 kDa, 9.5 kDa and 8.5 kDa constitute the F0 part of the complex. Our results show that polypeptide composition of the plant mitochondrial F0 differs from other eukaryotic F0 of yeast, mammals and chloroplasts.     

Functional analysis of hyperthermophilic endocellulase from Pyrococcus horikoshii by crystallographic snapshots

A hyperthermophilic membrane-related β-1,4-endoglucanase (family 5, cellulase) of the archaeon Pyrococcus horikoshii was found to be capable of hydrolysing cellulose at high temperatures. The hyperthermophilic cellulase has promise for applications in biomass utilization. To clarify its detailed function, we determined the crystal structures of mutants of the enzyme in complex with either the substrate or product ligands. We were able to resolve different kinds of complex structures at 1.65-2.01?? (1??=0.1?nm). The structural analysis of various mutant enzymes yielded a sequence of crystallographic snapshots, which could be used to explain the catalytic process of the enzyme. The substrate position is fixed by the alignment of one cellobiose unit between the two aromatic amino acid residues at subsites +1 and +2. During the enzyme reaction, the glucose structure of cellulose substrates is distorted at subsite -1, and the β-1,4-glucoside bond between glucose moieties is twisted between subsites -1 and +1. Subsite -2 specifically recognizes the glucose residue, but recognition by subsites +1 and +2 is loose during the enzyme reaction. This type of recognition is important for creation of the distorted boat form of the substrate at subsite -1. A rare enzyme-substrate complex was observed within the low-activity mutant Y299F, which suggested the existence of a trapped ligand structure before the formation by covalent bonding of the proposed intermediate structure. Analysis of the enzyme-substrate structure suggested that an incoming water molecule, essential for hydrolysis during the retention process, might be introduced to the cleavage position after the cellobiose product at subsites +1 and +2 was released from the active site.