A model of the quaternary structure of the Escherichia coli F1 ATPase from X-ray solution scattering and evidence for structural changes in the delta subunit during ATP hydrolysis

The shape and subunit arrangement of the Escherichia coli F1 ATPase (ECF1 ATPase) was investigated by synchrotron radiation x-ray solution scattering. The radius of gyration and the maximum dimension of the enzyme complex are 4.61 +/- 0.03 nm and 15.5 +/- 0.05 nm, respectively. The shape of the complex was determined ab initio from the scattering data at a resolution of 3 nm, which allowed unequivocal identification of the volume occupied by the alpha3beta3 subassembly and further positioning of the atomic models of the smaller subunits. The delta subunit was positioned near the bottom of the alpha3beta3 hexamer in a location consistent with a beta-delta disulfide formation in the mutant ECF1 ATPase, betaY331W:betaY381C:epsilonS108C, when MgADP is bound to the enzyme. The position and orientation of the epsilon subunit were found by interactively fitting the solution scattering data to maintain connection of the two-helix hairpin with the alpha3beta3 complex and binding of the beta-sandwich domain to the gamma subunit. Nucleotide-dependent changes of the delta subunit were investigated by stopped-flow fluorescence technique at 12 degrees C using N-[4-[7-(dimethylamino)-4-methyl]coumarin-3-yl]maleimide (CM) as a label. Fluorescence quenching monitored after addition of MgATP was rapid [k = 6.6 s-1] and then remained constant. Binding of MgADP and the noncleavable nucleotide analog AMP . PNP caused an initial fluorescent quenching followed by a slower decay back to the original level. This suggests that the delta subunit undergoes conformational changes and/or rearrangements in the ECF1 ATPase during ATP hydrolysis.     

Multipass diode-pumped Nd:YAG optical amplifiers at 1.06 μm and1.32 μm

We have built two versions of a diode-pumped Nd:YAG amplifier using a compact multipass confocal geometry with a fiber-coupled input. This confocal geometry provided efficient power and high gain in a volume of approximately 100 cm³. When pumped with a commercially mature 2 W 809 nm laser diode, the 1.06 μm version produced 460 mW and a small signal gain of 51 dB. The 1.32 μm version produced 170 mW and a small signal gain of 29 dB. Such an efficient amplifier, especially at 1.32 μm would be useful as a power booster in fiber optic telecommunications     

A smart pixel-based feedforward neural network

A novel smart pixel-based neural network was realized experimentally. The matrix multiplication is split into positive and negative components and computed optically. The necessary subtraction, binarization, and transmission of the resulting matrices is accomplished via a prototype smart pixel spatial light modulator. The result is a neural network that performs truly parallel computation without requiring the use of an external processor.     

Fundamental kinematical relationships for single-track vehicles

Kinematical considerations play an important role in the dynamic analysis of single-track vehicles. This paper deals with kinematical questions that must be faced in the course of every such analysis. A mathematical model is constructed; equations applicable whenever both wheels are in rolling contact with a plane supporting surface are developed; steady turning is analyzed; and results are discussed in detail.     

A critical strain model for the creep fracture of nickel-base superalloys

Fracture toughness samples of NIMONIC 115 were creep tested at 704°C in Mode I (tension) and Mode III (torsion) loading. In Mode III loading the rupture lives were two orders of magnitude shorter than in Mode I. The effects of loading mode are shown to agree with predictions based on a critical strain fracture model. Earlier test results with a number of different superalloys also are consistent with a strain controlled fracture model. Improved resistance to crack growth during creep at intermediate temperatures can be achieved by increasing Young’s modulus, yield strength, grain size and the critical strain value.     

Multiple mutations in cysA 14 MUTANTS OF Bacillus subtilis

Isolates of Bacillus subtilis that had been presumed to carry the cysA14 lesion have been studied. Our data indicate that these strains contain four mutations, all of which are linked by transformation and lie in the region of the ribosomal markers. The requirement for cysteine results from a defective serine transacetylase that is coded for by the cysA locus. Therefore, these mutants grow only in the presence of cysteine but not with sulfate, sulfite, or sulfide as the sole source of sulfur. A second genetic lesion (css) can be recognized by an increased sensitivity to the amino acid L-cysteine. The inhibited enzyme(s) has not been determined but inhibition is overcome by a mixture of eight amino acids. The third mutation (hts) results in the overproduction and excretion of hydrogen sulfide. This compound appears to be produced from cysteine by the enzyme cysteine desulfhydrylase and not by an increased activity of the sulfate-reductive pathway. This locus presumably codes for a regulatory element involved in the control of cysteine desulfhydrylase. The fourth mutation (cym) is not well characterized biochemically but results in a requirement for cysteine or methionine. The following order of these mutations has been established by transformation studies: hts, cysA, css, cym. The generally poor growth of these mutants in minimal-salts glucose media supplemented with cysteine can now be explained by these observations. The cysA14 mutants not only require an amino acid that is itself inhibitory to growth but they also overproduce the highly toxic compound hydrogen sulfide.