29,484 research outputs found

    Site-saturation studies of β-lactamase: Production and characterization of mutant β-lactamases with all possible amino acid substitutions at residue 71

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    A mutagenic technique that "saturates" a particular site in a protein with all possible amino acid substitutions was used to study the role of residue 71 in β-lactamase (EC 3.5.2.6). Threonine is conserved at residue 71 in all class A β-lactamases and is adjacent to the active site Ser-70. All 19 mutants of the enzyme were characterized by the penam and cephem antibiotic resistance they provided to Escherichia coli LS1 cells. Surprisingly, cells producing any of 14 of the mutant β-lactamases displayed appreciable resistance to ampicillin; only cells with mutants having Tyr, Trp, Asp, Lys, or Arg at residue 71 had no observable resistance to ampicillin. However, the mutants are less stable to cellular proteases than wild-type enzyme is. These results suggest that Thr-71 is not essential for binding or catalysis but is important for stability of the β-lactamase protein. An apparent change in specificity indicates that residue 71 influences the region of the protein that accommodates the side chain attached to the β-lactam ring of the substrate

    Bureau of Mines research on lunar resource utilization

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    Lunar resource utilization progra

    Insights into antibody catalysis: Structure of an oxygenation catalyst at 1.9-Ă… resolution

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    The x-ray crystal structures of the sulfide oxidase antibody 28B4 and of antibody 28B4 complexed with hapten have been solved at 2.2-Ă… and 1.9-Ă… resolution, respectively. To our knowledge, these structures are the highest resolution catalytic antibody structures to date and provide insight into the molecular mechanism of this antibody-catalyzed monooxygenation reaction. Specifically, the data suggest that entropic restriction plays a fundamental role in catalysis through the precise alignment of the thioether substrate and oxidant. The antibody active site also stabilizes developing charge on both sulfur and periodate in the transition state via cation-pi and electrostatic interactions, respectively. In addition to demonstrating that the active site of antibody 28B4 does indeed reflect the mechanistic information programmed in the aminophosphonic acid hapten, these high-resolution structures provide a basis for enhancing turnover rates through mutagenesis and improved hapten design

    Stochastic Transition Model for Discrete Agent Movements

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    We propose a calibrated two-dimensional cellular automaton model to simulate pedestrian motion behavior. It is a v=4 (3) model with exclusion statistics and random shuffled dynamics. The underlying regular grid structure results in a direction-dependent behavior, which has in particular not been considered within previous approaches. We efficiently compensate these grid-caused deficiencies on model level.Comment: 8 pages, 4 figure

    The Effects of JIT on the Development of Productivity Norms

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    Low inventory, or just-in-time (JIT) manufacturing systems, enjoy increasing application worldwide, yet the behavioral effects of such systems remain largely unexplored. Operations Research (OR) models of low inventory systems typically make a simplifying assumption that individual worker processing times are independent random variables. This leads to predictions that low-inventory systems will exhibit production interruptions. Yet empirical results suggest that low-inventory systems do not exhibit the predicted productivity losses. This paper develops a model integrating feedback, goal-setting, group cohesiveness, task norms, and peer pressure to predict how individual behavior may adjust to alleviate production interruptions in low-inventory systems. In doing so we integrate previous research on the development of task norms. Findings suggest that low-inventory systems induce individual and group responses that cause behavioral changes that mitigate production interruptions

    Ocean shrimp report 1977 season

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    Statewide Pacific ocean shrimp, Pandalus jordani, landings totaled 15,639,585 lb, more than triple the 1975 record catch of 4,992,233 lb. Record landings were recorded in Area A (Eureka-Crescent City), Area B-2 (Bodega Ray) with catches totaling 13,025,844 and 2,028,607 lb, respectively. Area B-1 (Fort Bragg) landings totaled 585,133 lb and no landings were reported from Area C (Avila-Morro Bay). In Area A the average catch per hour for the season for single-rig vessels was 1,241 lb and 2,228 lb for double-rig vessels. Area B-2 average catch per hour by the single-rig vessels was 2,536 lb. Two-year-old (1975 year class) shrimp dominated the catches in all areas. The outlook for the 1978 season in all areas is questionable because of the relatively weak showing of the incoming 1977 year class but it might make a significant contribution if abundant and of a marketable slze. (19pp.
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