Mitochondrial ATP synthase. Interaction of a synthetic 50-amino acid, beta-subunit peptide with ATP

Short and simple sequences favored the emergence of N-helix phospho-ligand binding sites in the first enzymes

The ubiquity of phospho-ligands suggests that phosphate binding emerged at the earliest stage of protein evolution. To evaluate this hypothesis and unravel its details, we identified all phosphate-binding protein lineages in the Evolutionary Classification of Protein Domains database. We found at least 250 independent evolutionary lineages that bind small molecule cofactors and metabolites with phosphate moieties. For many lineages, phosphate binding emerged later as a niche functionality, but for the oldest protein lineages, phosphate binding was the founding function. Across some 4 billion y of protein evolution, side-chain binding, in which the phosphate moiety does not interact with the backbone at all, emerged most frequently. However, in the oldest lineages, and most characteristically in αβα sandwich enzyme domains, N-helix binding sites dominate, where the phosphate moiety sits atop the N terminus of an α-helix. This discrepancy is explained by the observation that N-helix binding is uniquely realized by short, contiguous sequences with reduced amino acid diversity, foremost Gly, Ser, and Thr. The latter two amino acids preferentially interact with both the backbone amide and the side-chain hydroxyl (bidentate interaction) to promote binding by short sequences. We conclude that the first αβα sandwich domains emerged from shorter and simpler polypeptides that bound phospho-ligands via N-helix sites.

Autoantibodies to the adenosine triphosphate synthase play a pathogenetic role in Alzheimer's disease

It has become evident that an autoimmune component could play a role in Alzheimer's disease (AD) onset and/or progression. The aim of this study was to identify neuronal antigenic targets specifically recognized by serum autoantibodies and to investigate their cellular effects and their possible pathogenetic role. We identified, by an immunoproteomic approach using mouse brain proteins, the adenosine triphosphate (ATP) synthase β subunit as a new autoantigen in AD. Using an ELISA assay we found that serum anti-ATP synthase autoantibodies were present in 38% of patients with AD, but in no age-matched healthy subjects or in patients with Parkinson's disease or atherosclerosis. Analytical cytology studies, using SH-SY5Y neuroblastoma cell line, showed that ATP synthase autoantibodies were capable of inducing the inhibition of ATP synthesis, alterations of mitochondrial homeostasis and cell death by apoptosis. These findings suggest that autoantibodies specific to ATP synthase can exert a pathogenetic role via a mechanism that brings into play the impairment of the extracellular ATP homeostasis and the alteration of mitochondrial function triggering cell death by apoptosis.

Catalysis by isolated beta-subunits of the ATP Synthase/ATPase from Thermophilic bacillus PS3. Hydrolysis of pyrophosphate

Although the capacity of isolated beta-subunits of the ATP synthase/ATPase to perform catalysis has been extensively studied, the results have not conclusively shown that the subunits are catalytically active. Since soluble F(1) of mitochondrial H(+)-ATPase can bind inorganic pyrophosphate (PP(i)) and synthesize PP(i) from medium phosphate, we examined if purified His-tagged beta-subunits from Thermophilic bacillus PS3 can hydrolyze PP(i). The difference spectra in the near UV CD of beta-subunits with and without PP(i) show that PP(i) binds to the subunits. Other studies show that beta-subunits hydrolyze [(32)P] PP(i) through a Mg(2+)-dependent process with an optimal pH of 8.3. Free Mg(2+) is required for maximal hydrolytic rates. The Km for PP(i) is 75 microM and the Vmax is 800 pmol/min/mg. ATP is a weak inhibitor of the reaction, it diminishes the Vmax and increases the Km for PP(i). Thus, isolated beta-subunits are catalytically competent with PP(i) as substrate; apparently, the assembly of beta-subunits into the ATPase complex changes substrate specificity, and leads to an increase in catalytic rates.

Purification and properties of TrwB, a hexameric, ATP-binding integral membrane protein essential for R388 plasmid conjugation

TrwB is an integral membrane protein linking the relaxosome to the DNA transport apparatus in plasmid R388 conjugation. Native TrwB has been purified in monomeric and hexameric forms, in the presence of dodecylmaltoside from overexpressing bacterial cells. A truncated protein (TrwBDeltaN70) that lacked the transmembrane domain could be purified only in the monomeric form. Electron microscopy images revealed the hexameric structure and were in fact superimposable to the previously published atomic structure for TrwBDeltaN70. In addition, the electron micrographs showed an appendix, approximately 25 A wide, corresponding to the transmembrane region of TrwB. TrwB was located in the bacterial inner membrane in agreement with its proposed coupling role. Purified TrwB hexamers and monomers bound tightly the fluorescent ATP analogue TNP-ATP. A mutant in the Walker A motif, TrwB-K136T, was equally purified and found to bind TNP-ATP with a similar affinity to that of the wild type. However, the TNP-ATP affinity of TrwBDeltaN70 was significantly reduced in comparison with the TrwB hexamers. Competition experiments in which ATP was used to displace TNP-ATP gave an estimate of ATP binding by TrwB (K(d)((ATP)) = 0.48 mm for hexamers). The transmembrane domain appears to be involved in TrwB protein hexamerization and also influences its nucleotide binding properties.

Escherichia coli F1-ATPase subunit interactions: beta and gamma subunit peptides inhibit in vitro reconstitution of the active alpha beta gamma complex

For biochemical analysis of subunit interactions in the proton-translocating ATPase, a new approach with in vitro reconstitution of the Escherichia coli alpha beta gamma complex and the peptides derived from the subunits was established. Various portions of the beta or gamma subunits were used for in vitro reconstitution of the alpha beta gamma complex from the purified subunits. For the beta subunits, peptides corresponding to residues 226-459, 254-459, and 226-365 inhibited reconstitution, while those corresponding to residues 1-105, 1-146, and 295-459 did not. For the gamma subunits, peptides corresponding to residues 1-192 and 74-286 exhibited inhibitory effect on reconstitution, but the peptide containing residues 191-286 did not. Only inhibitory peptides blocked the assembly of the alpha beta gamma complex which was detected by nondenaturing polyacrylamide gel electrophoresis. These inhibitory peptides bound to the alpha or beta subunit on the filter, but the noninhibitory peptides did not. These results suggested that regions beta 254-294 and gamma 74-190 have sequences important for subunit interactions which interfered with those in the reconstitution mixtures. Based on comparison between X-ray crystallographic data of bovine alpha beta gamma complex and the present results, we discussed here the significance of the biochemical approach adopted in this study.

Binding and hydrolysis of TNP-ATP by Escherichia coli F1-ATPase

It had previously been suggested that Vmax hydrolysis rate of 2', 3'-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate (TNP-ATP) by F1-ATPase required filling of only two catalytic sites on the enzyme (Grubmeyer, C., and Penefsky, H. S. (1981) J. Biol. Chem. 256, 3718-3727), whereas recently it was shown that Vmax rate of ATP hydrolysis requires that all three catalytic sites are filled (Weber, J., Wilke-Mounts, S., Lee, R. S. F., Grell, E., and Senior, A. E. (1993) J. Biol. Chem. 268, 20126-20133). To resolve this apparent discrepancy, we measured equilibrium binding and hydrolysis of MgTNP-ATP under identical conditions, using betaY331W mutant Escherichia coli F1-ATPase, in which the genetically engineered tryptophan provides a direct fluorescent probe of catalytic site occupancy. We found that MgTNP-ATP hydrolysis at Vmax rate did require filling of all three catalytic sites, but in contrast to the situation with MgATP, "bisite hydrolysis" of MgTNP-ATP amounted to a substantial fraction (approximately 40%) of Vmax. Binding of MgTNP-ATP to the three catalytic sites showed strong binding cooperativity (Kd1 < 1 nm, Kd2 = 23 nm, Kd3 = 1.4 microM). Free TNP-ATP (i.e. in presence of EDTA) bound to all three catalytic sites with lower affinity but was not hydrolyzed. These data emphasize that the presence of Mg2+ is critical for cooperativity of substrate binding, formation of the very high affinity first catalytic site, and hydrolytic activity in F1-ATPases and that these three properties are strongly correlated.

Synthesis of medium pyrophosphate by soluble mitochondrial F1 through dimethyl sulfoxide-water transitions

Soluble F1 from heart mitochondria incubated in mixtures that have Mg2+, inorganic phosphate, and dimethyl sulfoxide (40% (v/v)) catalyzes the spontaneous synthesis of ATP and pyrophosphate (Tuena de Gómez-Puyou, M., García, J. J., and Gómez-Puyou, A. (1993) Biochemistry 32, 2213-2218). By filtration techniques, it was determined that synthesized ATP and pyrophosphate are enzyme bound, albeit the affinity for pyrophosphate was lower than that of ATP. After ATP and pyrophosphate were formed in dimethyl sulfoxide mixtures, dilution with aqueous buffer to a dimethyl sulfoxide concentration of 6.0% brought about the partition of pyrophosphate into the media. This was evidenced by filtration experiments as well as by the accessibility of synthesized pyrophosphate to soluble inorganic pyrophosphatase. Release of pyrophosphate induced by dilution occurred in less than 15 s. Under conditions that produce release of pyrophosphate, no release of ATP was observed; instead, ATP underwent hydrolysis. Studies on the effect of arsenate on the synthesis and hydrolysis of ATP and PPi in F1 showed that hydrolysis of synthesized PPi at its site of synthesis was slower than that of ATP. Thus, the question of whether differences in the rates of hydrolysis accounted for the dilution-induced release of PPi but not of ATP was addressed. Synthesis and hydrolysis of ATP and pyrophosphate were examined in preparations of soluble F1 in complex with its inhibitor protein; the complex had an ATPase activity about 100 times lower than that of free F1. In mixtures that contained dimethyl sulfoxide, the complex synthesized ATP and pyrophosphate at nearly the same rates; upon dilution, hydrolysis of both compounds occurred also at similar rates, yet only pyrophosphate was released. The same phenomenon was observed in F1 that had been depleted of adenine nucleotides. Hence, dilution-induced release of PPi was independent of the overall catalytic properties of the enzyme or its content of adenine nucleotides. Since synthesis of ATP occurs at the expense of the ADP that remains after depletion of adenine nucleotides, it is likely that the failure of ATP to be released is due to the high affinity that F1 exhibits for the synthesized ATP. Nevertheless, the results illustrate that a complete catalytic cycle that starts with medium Pi and ends with medium pyrophosphate may be reproduced in soluble mitochondrial F1.

Lowered temperature or binding of pyrophosphate to sites for noncatalytic nucleotides modulates the ATPase activity of the beef heart mitochondrial F1-ATPase by decreasing the affinity of a catalytic site for inhibitory MgADP

Lineweaver-Burk plots for ATP hydrolysis catalyzed by bovine heart mitochondrial F1-ATPase (MF1) at 30 degrees C are biphasic, whereas they are linear at 15 degrees C. The rate of inactivation of the enzyme at 23 degrees C by 5'-[(p-fluorosulfonyl)benzoyl]adenosine (FSBA), which derivatizes noncatalytic nucleotide binding sites, is about 4 times faster when loss of activity is monitored at 15 degrees C as opposed to 30 degrees C. This suggests that maximal loss of ATPase monitored at 15 degrees C is observed when a single noncatalytic site is derivatized, whereas maximal inactivation at 30 degrees C requires modification of three noncatalytic sites. Prior incubation of MF1 depleted of endogenous nucleotides (nd-MF1) with pyrophosphate (PPi) stimulates ATPase activity 2-fold when assayed at 30 degrees C and pH 8.0. This stimulation correlates with binding of [32P]PPi to the second and third binding sites for PPi to be filled. Prior binding of PPi to nd-MF1 increases the rate of inactivation of the enzyme by FSBA at 23 degrees C about 4-fold when loss of activity is monitored at 30 degrees C and pH 8.0, whereas it does not affect the rate of inactivation when loss of ATPase is monitored at 15 degrees C or loss of ITPase is monitored at 30 degrees C. This indicates that the accelerated rate of inactivation induced by PPi when assays are conducted at 30 degrees C is not due to an increased rate of derivatization of noncatalytic sites. After 85% inactivation with FSBA, nd-MF1 retains the capacity to bind 2.8 mol of [32P]PPi per mole.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo affinity label of a protein expressed in Escherichia coli. Coenzyme A occupied the AT(D)P binding site of the mutant F1-ATPase beta subunit (Y307C) through a disulfide bond

When Tyr-307 of the beta subunit of F1-ATPase from a thermophilic Bacillus strain PS3 is replaced by cysteine and expressed in Escherichia coli cells, about a half population of the mutant beta subunit are labeled by Coenzyme A at Cys-307 through a disulfide bond which is cleavable by reducing treatment. The mutant beta subunit can be reconstituted into the alpha 3 beta 3 complex of which ATPase activity is stimulated two-fold by reducing treatment either prior or after reconstitution. Since Tyr-307 has been supposed to be located at one of subdomains which form the ATP binding site of the beta subunit, Coenzyme A binds to the mutant beta subunit as an AT(D)P analogue in E. coli cells and then covalently attaches to Cys-307.

Genetic and biochemical analysis of Salmonella typhimurium FliI, a flagellar protein related to the catalytic subunit of the F0F1 ATPase and to virulence proteins of mammalian and plant pathogens

FliI is a Salmonella typhimurium protein that is needed for flagellar assembly and may be involved in a specialized protein export pathway that proceeds without signal peptide cleavage. FliI shows extensive sequence similarity to the catalytic beta subunit of the F0F1 ATPase (A. P. Volger, M. Homma, V. M. Irikura, and R. M. Macnab, J. Bacteriol. 173:3564-3572, 1991). It is even more similar to the Spa47 protein of Shigella flexneri (M. M. Venkatesan, J. M. Buysse, and E. V. Oaks, J. Bacteriol. 174:1990-2001, 1992) and the HrpB6 protein of Xanthomonas campestris (S. Fenselau, I. Balbo, and U. Bonas, Mol. Plant-Microbe Interact. 5:390-396, 1992), which are believed to play a role in the export of virulence proteins. Site-directed mutagenesis of residues in FliI that correspond to catalytically important residues in the F1 beta subunit resulted in loss of flagellation, supporting the hypothesis that FliI is an ATPase. FliI was overproduced and purified almost to homogeneity. It demonstrated ATP binding but not hydrolysis. An antibody raised against FliI permitted detection of the protein in wild-type cells and an estimate of about 1,500 subunits per cell. An antibody directed against the F1 beta subunit of Escherichia coli cross-reacted with FliI, confirming that the proteins are structurally related. The relationship between three proteins involved in flagellar assembly (FliI, FlhA, and FliP) and homologs in a variety of virulence systems is discussed.

Synthesis of pyrophosphate and ATP by soluble mitochondrial F1

Soluble F1 from beef heart that has been depleted of adenine nucleotides to values of 0.4 mol of ADP and 0.1 mol ATP/mol of enzyme has the capacity to synthetize about 0.1 mol of ATP/mol of enzyme from medium phosphate in the presence of Mg2+ and 30% dimethyl sulfoxide. Under the same conditions, native and adenine nucleotide depleted F1 can also synthesize pyrophosphate to values that range from 0.03 to 0.05 mol/mol of F1. The formation of pyrophosphate requires Mg2+ and dimethyl sulfoxide. The formed pyrophosphate remains bound to F1 during filtration through Sephadex centrifugation columns. In all water media, adenine nucleotide depleted, but not native, F1 can hydrolyze pyrophosphate to values of about 0.2 nmol min-1 mg-1. This activity is inhibited or stimulated by agents (adenylyl imidodiphosphate, aurovertin, and methanol) that produce such effects on the ATPase activity of F1; NaN3 stimulated the activity. Therefore, F1 from bovine heart mitochondria has the capacity to catalyze synthesis and hydrolysis of ATP. Synthesis of pyrophosphate by the soluble F1 appears to follow the same energetic considerations that have been postulated for ATP synthesis by the soluble enzyme [de Meis (1989) Biochim. Biophys. Acta 973, 339-349].

Two-dimensional NMR, circular dichroism, and fluorescence studies of PP-50, a synthetic ATP-binding peptide from the beta-subunit of mitochondrial ATP synthase

PP-50, a peptide based on residues 141-190 of the beta-subunit of mitochondrial F1-ATPase, contains the GX4GKT consensus region for nucleoside triphosphate binding and has been shown to bind ATP [Garboczi, D.N., Shenbagamurthi, W.K., Hullihen, J., & Pedersen, P.L. (1988) J. Biol. Chem. 263, 812-816]. At pH 4.0, appropriate for NMR studies, PP-50 retains the ability to bind ATP tightly (KD = 17.5 microM) with a 1:1 stoichiometry as shown by titrations measuring the partial quenching of ATP fluorescence by PP-50. CD spectra of PP-50 at pH 4.0 and at low ionic strength show 5.8% helix, 30.2% beta-structure, and 64% coil. ATP binding increases the structure of PP-50, changing the CD to 7.5% helix, 44.5% beta-structure, and 48% coil. Increasing the ionic strength to 50 mM KCl also increases the structure, changing the CD to 7.4% helix, 64.4% beta-structure, and 28.2% coil. The 600-MHz proton NMR spectrum of PP-50, at pH 4.0 and low ionic strength, has been assigned by 2D methods (TOCSY, DQF-COSY, and NOESY with jump-return water suppression). Based on strong d alpha N NOEs, J alpha N values, and NH chemical shifts differing from random coil values, regions of extended structure are detected from residues 1-7 and 43-48. Based on dNN, dNN(i,i+2), and d alpha N(i,i+2) NOEs and 3J alpha N values, possible type I' and type I turns are found from residues 11-14 and 31-34, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Stoichiometric binding of 2'(or 3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate to bovine heart cytochrome c oxidase

The binding of 2'(or 3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate (TNP-ATP) to isolated bovine heart cytochrome c oxidase (COX) was studied by following its specific spectral change at 510 nm. The quantitative titration revealed two binding sites for TNP-ATP per monomer COX with a Kd of 1.6 microM.

The ATP synthase (F0-F1) complex in oxidative phosphorylation

The transmembrane electrochemical proton gradient generated by the redox systems of the respiratory chain in mitochondria and aerobic bacteria is utilized by proton translocating ATP synthases to catalyze the synthesis of ATP from ADP and P(i). The bacterial and mitochondrial H(+)-ATP synthases both consist of a membranous sector, F0, which forms a H(+)-channel, and an extramembranous sector, F1, which is responsible for catalysis. When detached from the membrane, the purified F1 sector functions mainly as an ATPase. In chloroplasts, the synthesis of ATP is also driven by a proton motive force, and the enzyme complex responsible for this synthesis is similar to the mitochondrial and bacterial ATP synthases. The synthesis of ATP by H(+)-ATP synthases proceeds without the formation of a phosphorylated enzyme intermediate, and involves co-operative interactions between the catalytic subunits.

Over-expression and refolding of beta-subunit from the chloroplast ATP synthase

We established a bacterial system for high-level over-expression of the spinach chloroplast atpB gene which encodes the ATP synthase beta subunit. Upon induction, atpB was expressed as at least 50% to 70% of total cell protein. Although the over-expressed beta polypeptide formed insoluble inclusion bodies, more than fifty percent of it was restored to a functional form by solubilizing the inclusion bodies with 4 M urea and slowly removing the urea by stepwise dialysis. The resulting beta subunit exhibited specific and selective nucleotide binding properties identical to those of the native beta subunit.

Cystic fibrosis transmembrane conductance regulator: nucleotide binding to a synthetic peptide

Multiple mutations in the gene responsible for cystic fibrosis are located within a region predicted to encode a nucleotide-binding fold in the amino terminal half of the cystic fibrosis transmembrane conductance regulator protein. A 67-amino acid peptide (P-67) that corresponds to the central region of this putative nucleotide binding site was chemically synthesized and purified. This peptide bound adenine nucleotides. The apparent dissociation constants (Kd's) for the trinitrophenyl (TNP) adenine nucleotides, TNP-adenosine triphosphate, TNP-adenosine diphosphate, and TNP-adenosine monophosphate, were 300 nanomolar, 200 nanomolar, and greater than 1 micromolar, respectively. The Kd for adenosine triphosphate was 300 micromolar. Circular dichroism spectroscopy was used to show that P-67 assumes a predominantly beta sheet structure in solution, a finding that is consistent with secondary structure predictions. On the basis of this information, the phenylalanine at position 508, which is deleted in approximately 70 percent of individuals with cystic fibrosis, was localized to a beta strand within the nucleotide binding peptide. Deletion of this residue is predicted to induce a significant structural change in the beta strand and altered nucleotide binding.

Selectivity of modification when latent and activated forms of the chloroplast F1-ATPase are inactivated by 7-chloro-4-nitrobenzofurazan

The characteristics and specificity of inactivation of the chloroplast F1-ATPase (CF1) with 7-chloro-4-nitrobenzofurazan (Nbf-Cl) have been investigated. Inactivation of the octylglucoside-dependent Mg2+-ATPase activity of latent CF1 by Nbf-Cl can be correlated with the formation of about 1.2 mol of Nbf-O-Tyr per mole of enzyme. Following inactivation of CF1 with [14C]Nbf-Cl, polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed that the majority of the radioactive reagent incorporated is present in the beta subunit. Treatment of the enzyme with [14C]Nbf-Cl following dithiothreitol heat activation, led to similar labeling of the beta subunit and substantial incorporation of 14C into the gamma subunit. On complete inactivation, about 4 mol of Nbf-S-Cys is formed per mole of dithiothreitol-heat-activated CF1. Incorporation of 14C into the gamma subunit is prevented by prior treatment of the latent CF1 or of the dithiothreitol-heat-activated CF1 with iodoacetamide. Following incubation of the dithiothreitol-heat-activated CF1 with iodoacetamide, complete inactivation of the octylglucoside-dependent Mg2+-ATPase activity by Nbf-Cl can be correlated with the formation of about 1.2 mol of Nbf-O-Tyr per mole of enzyme. After stabilization of the [14C]Nbf-O-Tyr derivative by treatment with sodium dithionite, a labeled peptide was purified. Automatic Edman degradation of this peptide revealed the sequence V-X-V-P-A-D-(D). The majority of the radioactivity was cleaved in the second cycle, the position occupied in CF1 by Tyr-beta-328, which is homologous to Tyr-beta-311, the residue reactive with Nbf-Cl in the beef heart mitochondrial F1-ATPase. When CF1, modified at Tyr-beta-328 with Nbf-Cl, is incubated at pH 9.0, the Nbf-O-Tyr adduct is hydrolyzed, leading to concomitant recovery of the ATPase activity. In double labeling experiments, two-dimensional isoelectric focusing in the presence of urea followed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate indicates that 2-azido-ADP, covalently bound at the tight ADP binding site, and the tyrosine modified by [14C]Nbf-Cl are located in different beta subunits.

ATP synthases--structure of the F1-moiety and its relationship to function and mechanism

A great deal of progress has been made in understanding both the structure and the mechanism of F1-ATPase. The primary structure is now fully known for at least five species. Sequence comparison between chloroplast, photobacteria, aerobic bacteria, and mitochondrial representatives allow us to infer more general functional relationships and evolutionary trends. Although the F1 moiety is the most studied segment of the H+-ATPase complex, there is not a full understanding of the mechanism and regulation of its hydrolytic activity. The beta subunit is now known to contain one and probably two nucleotide binding domains, one of which is believed to be a catalytic site. Recently, two similar models have been proposed to attempt to describe the "active" part of the beta subunits. These models are mainly an attempt to use the structure of adenylate kinase to represent a more general working model for nucleotide binding phosphotransferases. Labelling experiments seem to indicate that several critical residues outside the region described by the "adenylate kinase" part of this model are also actively involved in the ATPase activity. New models will have to be introduced to include these regions. Finally, it seems that a consensus has been reached with regard to a broad acceptance of the asymmetric structure of the F1-moiety. In addition, recent experimental evidence points toward the presence of nonequivalent subunits to describe the functional activity of the F1-ATPase. A summary diagram of the conformational and binding states of the enzyme including the nonequivalent beta subunit is presented. Additional research is essential to establish the role of the minor subunits--and of the asymmetry they introduce in F1--on the physiological function of the enzyme.

E. coli F1-ATPase: site-directed mutagenesis of the beta-subunit

Residues beta Glu-181 and beta Glu-192 of E. coli F1-ATPase (the DCCD-reactive residues) were mutated to Gln. Purified beta Gln-181 F1 showed 7-fold impairment of 'unisite' Pi formation from ATP and a large decrease in affinity for ATP. Thus the beta-181 carboxyl group in normal F1 significantly contributes to catalytic site properties. Also, positive catalytic site cooperativity was attenuated from 5 X 10(4)- to 548-fold in beta Gln-181 F1. In contrast, purified beta Gln-192 F1 showed only 6-fold reduction in 'multisite' ATPase activity. Residues beta Gly-149 and beta Gly-154 were mutated to Ile singly and in combination. These mutations, affecting residues which are strongly conserved in nucleotide-binding proteins, were chosen to hinder conformational motion in a putative 'flexible loop' in beta-subunit. Impairment of purified F1-ATPase ranged from 5 to 61%, with the double mutant F1 less impaired than either single mutant. F1 preparations containing beta Ile-154 showed 2-fold activation after release from membranes, suggesting association with F0 restrained turnover on F1 in these mutants.