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11.
Serpins, serine proteinase inhibitors, form enzymatically inactive, 1:1 complexes (denoted E*I*) with their target proteinases, that only slowly release I*, in which the P1-P1' linkage is cleaved. Recently we presented evidence that the serpin antichymotrypsin (ACT, I) reacts with the serine proteinase chymotrypsin (Chtr, E) to form an E*I* complex via a three-step mechanism, E + I <==> E .I <==> EI' <==> E*I* in which EI', which retains the P1-P1' linkage, is formed in a partly or largely rate-determining step, depending on temperature (O'Malley, K. H, Nair, S. A., Rubin, H., and Cooperman, B. S. (1997) J. Biol. Chem. 272, 5354-5359). Here we extend these studies through the introduction of a new assay for the formation of the postcomplex fragment, corresponding to ACT residues 359 (the P1' residue) to 398 (the C terminus), coupled with rapid quench flow kinetic analysis. We show that the E.I encounter complex of wild type-rACT and Chtr forms both E*I* and postcomplex fragment with the same rate constant, so that both species arise from EI' conversion to E*I*. These results support our earlier conclusion that the P1-P1' linkage is preserved in EI' and imply that E*I* corresponds to a covalent adduct of E and I, either acyl enzyme or the tetrahedral intermediate formed by water attack on acyl enzyme. Furthermore, we show that the A347R (P12) variant of rACT, which is a substrate rather than an inhibitor of Chtr, has a rate constant for postcomplex fragment formation from the E.I complex very similar to that observed for WT-rACT, implying that EI' is the common intermediate from which partitioning to inhibitor and substrate pathways occurs. These results are used to elaborate a proposed scheme for ACT interaction with Chtr that is considered in the light of relevant results from studies of other serpin-serine proteinase pairs. 相似文献
12.
13.
CM Lukacs JQ Zhong MI Plotnick H Rubin BS Cooperman DW Christianson 《Canadian Metallurgical Quarterly》1996,3(10):888-893
A hallmark of serpin function is the massive beta-sheet rearrangement involving the insertion of the cleaved reactive loop into beta-sheet A as strand s4A. This structural transition is required for inhibitory activity. Small hydrophobic residues at P14 and P12 positions of the reactive loop facilitate this transition, since these residues must pack in the hydrophobic core of the cleaved serpin. Despite the radical substitution of arginine at the P12 position, the crystal structure of cleaved A347R antichymotrypsin reveals full strand s4A insertion with normal beta-sheet A geometry; the R347 side chain is buried in the hydrophobic protein core. In contrast, the structure of cleaved P14 T345R antichymotrypsin reveals substantial yet incomplete strand s4A insertion, without burial of the R345 side chain. 相似文献
14.
Removal of retained foreign bodies can be a tedious process, requireing considerable skill and ingenuity on the part of the surgeon. Employment of a curved, double-pronged, uterine vulsellum can be useful in simplifying removal of certain of these objects. A method which can be employed on an outpatient basis is described. When this method fails, suitable cooperation by the patient is lacking, or there is evidence of serious rectal injury or perforation, hospitalization for appropriate treatment under general or regional anesthesia is indicated. 相似文献
15.
Gastric emptying--physiology and measurements 总被引:1,自引:0,他引:1
16.
Hamann CS; Lentainge S; Li LS; Salem JS; Yang FD; Cooperman BS 《Protein engineering, design & selection : PEDS》1998,11(3):219-224
Here we report on the formation and activity of complexes between the large
subunit (mR1) dimer of mouse ribonucleotide reductase (mRR) and small
subunit chimeric dimers (cR2) derived from Escherichia coli and mouse small
subunits. cR2 subunits were constructed by substituting mouse C-terminal
gene sequences, coding for either 7 or 33 amino acid residues, for the
corresponding E.coli R2 (eR2) sequences, with the remainder of the gene
corresponding to eR2. The purified cR2s contained the micro-oxo bridged
diferric center and tyrosine radical necessary for reductase activity,
although the radical signal was broadened compared with wild-type eR2.
Neither chimera formed an active complex with mR1, but each was a
competitive inhibitor, with respect to mR2, of mRR activity. The inhibition
constants for both chimeras were similar, and were sevenfold higher than
the dissociation constant of mR2 dimer to mR1 dimer (0.24 +/- 0.02 microM).
Analysis of inhibition data showed that chimeric R2 subunits bind to
mammalian R1 with a 1:1 (R1:R2) stoichiometry and permit the inference that
both C-termini in a cR2 dimer bind to the two sites per mR1 dimer. The lack
of enzymatic activity in the mR1-cR2 complex is attributed to perturbation
or elimination of interactions linking the tyrosine radical/dinuclear iron
center and the C-terminus within R2.
相似文献
17.
The number of moves required to solve any configuration of Rubik’s cube has held a fascination for over 25 years. A new upper bound of 26 is produced. More important, a new methodology is described for finding upper bounds. The novelty is two-fold. First, parallel disks are employed. This allows 1.4×1012 states representing symmetrized cosets to be enumerated in seven terabytes. Second, a faster table-based multiplication is described for symmetrized cosets that attempts to keep most tables in the CPU cache. This enables the product of a symmetrized coset by a generator at a rate of 10 million moves per second. 相似文献
18.
Bond Meg A.; Punnett Laura; Pyle Jean L.; Cazeca Dianne; Cooperman Manuela 《Canadian Metallurgical Quarterly》2004,9(1):28
This cross-sectional study of nonfaculty university employees examined associations among gendered work conditions (e.g., sexism and discrimination), job demands, and employee job satisfaction and health. Organizational responsiveness and social support were examined as effect modifiers. Comparisons were made by gender and by the male-female ratio in each job category. The relationship of gendered conditions of work to outcomes differed on the basis of respondents' sex and the job sex ratio. Although the same predictors were hypothesized for job satisfaction, physical health, and psychological distress, there were some differing results. The strongest correlate of job satisfaction was social support; perceived sexism in the workplace also contributed for both men and women. Organizational factors associated with psychological distress differed between female- and male-dominated jobs. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
19.
Twenty-four insulin-dependent diabetic children and 114 normal control children, all between the ages of 6 to 16 years, were investigated for riboflavin deficiency. The method used was a measurement of erythrocyte glutathione reductase activity and the results were expressed as the activity coefficient (AC). None of the children had received vitamin supplementation. The percentage of diabetic children with riboflavin deficiency was 4 fold greater than in non diabetics. Supplementation with daily oral riboflavin quickly returned all AC values to normal. 相似文献
20.
Omer Khalid Guangbo Hao Hamish MacDonald Aubryn Cooperman Fiona Devoy McAuliffe Cian Desmond 《风能》2024,27(2):152-164
Operations and maintenance (O&M) of floating offshore wind farms (FOWFs) poses various challenges in terms of greater distances from the shore, harsher weather conditions, and restricted mobility options. Robotic systems have the potential to automate some parts of the O&M leading to continuous feature-rich data acquisition, operational efficiency, along with health and safety improvements. There remains a gap in assessing the techno-economic feasibility of robotics in the FOWF sector. This paper investigates the costs and benefits of incorporating robotics into the O&M of a FOWF. A bottom-up cost model is used to estimate the costs for a proposed multi-robot platform (MRP). The MRP houses unmanned aerial vehicle (UAV) and remotely operated vehicle (ROV) to conduct the inspection of specific FOWF components. Emphasis is laid on the most conducive O&M activities for robotization and the associated technical and cost aspects. The simulation is conducted in Windfarm Operations and Maintenance cost-Benefit Analysis Tool (WOMBAT), where the metrics of incurred operational expenditure (OPEX) and the inspection time are calculated and compared with those of a baseline case consisting of crew transfer vessels, rope-access technicians, and divers. Results show that the MRP can reduce the inspection time incurred, but this reduction has dependency on the efficacy of the robotic system and the associated parameterization e.g., cost elements and the inspection rates. Conversely, the increased MRP day rate results in a higher annualized OPEX. Residual risk is calculated to assess the net benefit of incorporating the MRP. Furthermore, sensitivity analysis is conducted to find the key parameters influencing the OPEX and the inspection time variation. A key output of this work is a robust and realistic framework which can be used for the cost-benefit assessment of future MRP systems for specific FOWF activities. 相似文献