Preferential interaction parameters for F1 -ATPase from a thermophilic bacterium (PS3)

Structure of phenylbutazone and mofebutazone in the crystalline state and in solution

The crystal structure of the keto form of phenylbutazone has been determined and compared with the molecular conformation of mofebutazone. The pronounced differences between these two structures are the conformation of the n-butyl side chain (which is extended and in trans conformation for mofebutazone, however, bent at the C gamma-position with hydrogen bonding of the gamma-hydrogen to the carbonyl C(3)--O(1) for phenylbutazone), and the in-plane conformation of the phenyl group with respect to the heterocyclic ring system in mofebutazone compared with two benzene rings at N(1) and N(2) which are almost perpendicular to the pyrazolidin-(3,5)-dione ring. Preliminary X-ray data reveal that the structures of the alkali enolates of both compounds are difficult to solve because the crystal quality is insufficient and highly disordered. However, the large unit cells are consistent with chelated structures of the alkali enolates with solvent. Sodium and potassium enolates of phenylbutazone in nonpolar solvents (e.g., benzene and cyclohexane) exist as inverse micelles comprised of 30-40 monomer units. In contrast, the salt appears to be essentially monomeric in 1,2-dimethoxyethane, and, in water for phenylbutazone, the critical micelle concentration (CMC) is greater than 0.30 M. Mofebutazone salts, however, reveal a CMC of 1.5 X 10(-3) M in water, where the basic unit of micellar aggregation seems to be the dimer. The micellar properties of phenylbutazone and mofebutazone enolates are strongly dependent on the nature of solvents, solvation of the enolate, and size of the cation. However, sodium and potassium enolates of mofebutazone in nonpolar solvents exist as small inverse micelles comprised of 8-10 monomer units only. However, in aqueous solution, weight average molecular weights of 13,100 +/- 500 were determined, with a radius of gyration of 12.85 +/- 0.55 A.

Structural aspects and orientation mechanism of mitochondrial F1 adenosinetriphosphatase. Evidence for a negative electric birefringence due to a permanent moment perpendicular to the long axes of the particle

The electric birefringence technique was used to investigate the steady-state birefringence, the orientational relaxation time, and the orientation mechanism of pig heart mitochondrial F1 adenosine-5'-triphosphatase (F1-ATPase). The electrooptical properties of this enzyme in solution were studied as functions of pH, protein concentration, and applied electric field. The F1-ATPase exhibits a surprising negative electric birefringence with a specific Kerr constant of -1.5 X 10(-3) esu cgs. The field-independent relaxation time was found to be 0.65 +/- 0.05 microseconds, corresponding to a rotational diffusion constant of 2.55 X 10(5) s-1. The overall size and shape of F1-ATPase have been calculated from both translational and rotational diffusion constants. The enzyme may be assumed to be an oblate ellipsoid of revolution with dimensions of about 170 X 170 X 70 A. The orientation mechanism of F1-ATPase was analyzed by fitting experimental birefringence rising curves with theoretical rising functions. The ratio of the permanent to induced dipole moment is found to be very high; therefore, the birefringence of F1-ATPase is due to a strong permanent dipole moment in a direction perpendicular to the long axes of the particle. These particular electric properties can be explained by the oligomeric structure of the protein and seem likely to play a role in its mechanism of functioning.

Photosynthetic ATPases: purification, properties, subunit isolation and function

Photosynthetic coupling factor ATPases (F1-ATPases) generally censist of five subunits named α, β, γ, δ and ε in order of decreasing apparent molecular weight. The isolated enzyme has a molecular weight of between 390,000 to 400,000, with the five subunits probably occurring in a 3:3:1:1:1 ratio. Some photosynthetic F1 ATPases are inactive as isolated and require treatment with protease, heat or detergent in order to elicit ATPase activity. This activity is sensitive to inhibition by free divalent cations and appears to be more specific for Ca(2+) vs. Mg(2+) as the metal ion substrate chelate. This preference for Ca(2+) can be explained by the higher inhibition constant for inhibition of ATPase activity by free Ca(2+). Methods for the assay of a Mg-dependent ATPase activity have recently been described. These depend on the presence of organic solvents or detergents in the reaction mixture for assay. The molecular mechanism behind the expression of either the Ca- or Mg-ATPase activities is unknown. F1-ATPases function to couple proton efflux from thylakoid membranes or chromatophores to ATP synthesis. The isolated enzyme may thus also be assayed for the reconstitution of 'coupling activity' to membranes depleted of coupling factor 1.The functions of the five subunits in the complex have been deduced from the results of chemical modification and reconstitution studies. The δ subunit is required for the functional binding of the F1 to the F0. The active site is probably contained in the β (and α) subunit(s). The proposed functions for the γ and ε subunits are, however, still matters of controversy. Coupling factors from a wide variety of species including bacteria, algae, C3 and C4 plants, appear to be immunologically related. The β subunits are the most strongly related, although the α and γ subunits also show significant immunological cross-reactivity. DNA sequence analyses of the genes for the β subunit of CF1 have indicated that the primary sequence of this polypeptide is highly conserved. The genes for the polypeptides of CF1 appear to be located in two cellular compartments. The α, β and ε subunits are coded for on chloroplast DNA, whereas the γ and δ subunits are probably nuclear encoded. Experiments involving protein synthesis by isolated chloroplasts or protein synthesis in the presence of inhibitors specific for one or the other set of ribosomes in the cell suggest the existence of pools of unassembled CF1 subunits. These pools, if they do exist in vivo, probably make up no greater than 1% of the total CF1 content of the cell.