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The bacterial chemotaxis protein CheY is activated in vivo by the covalent
phosphorylation of a single aspartate residue at position 57. However, this
phosphate linkage is unstable (t1/2 approximately 20 s at room
temperature), thereby precluding many biochemical analyses. Here we present
a synthetic scheme to prepare an analog of CheY-phosphate (Che Y-P) with
chemical stability of the phosphate linkage enhanced by several orders of
magnitude relative to the native protein. Starting with CheY D57C, a
site-specific mutant of CheY with a unique cysteine residue in place of the
aspartate at position 57, two sequential disulfide exchange reactions were
performed to form the final product 'CheY D57C-SPO3' with a thiophosphate
moiety covalently bonded to the protein in a disulfide linkage. Mass
spectral analysis showed that the desired analog was present at 70-80% of
the total protein. The disulfide linkage had a t1/2 of 8 days at 4 degrees
C. Biochemical characterization of CheY D57C-SPO3 included assessment of
conformational properties using tryptophan fluorescence, evaluation of
metal binding properties and measurement of binding interactions with the
chemotaxis proteins CheZ and FliM. Despite possessing a phosphoryl group at
a nearly identical location as native CheY-phosphate, the analog was unable
to emulate CheY-phosphate function, thereby supporting the idea that there
are very precise geometric requirements for successful CheY activation.
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The Minnesota Multiphasic Personality Inventory—2 (MMPI—2) Validity scales (L, F, and K) were used to identify subgroups of inpatients seeking treatment for alcoholism and to determine the extent that assessed test-taking attitude could be generalized to other alcoholism assessment instruments. Cluster analysis of the inpatients receiving treatment for alcoholism identified 3 distinct response style subgroups: defensive, straightforward, and exaggerated. These patterns were confirmed in a 2nd sample. Calibration equations were generated and used to classify a subsequent sample into subgroups, and expected differences were found across the subgroups on the Alcohol Use Inventory (J. L. Horn, K. W. Wanberg, & F. M. Foster, 1987) and the Inventory of Drinking Situations (H. M. Annis, 1982). These preliminary results suggest that MMPI—2 response style is associated with response to other alcohol abuse assessment instruments. Future research examining the relationship between test-taking attitude and treatment involvement and outcome is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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Low-Noise Mid-Wavelength Infrared Avalanche Photodiodes 总被引:1,自引:0,他引:1
Siddhartha Ghosh Shubhrangshu Mallick Koushik Banerjee Christoph Grein Silviu Velicu Jun Zhao Don Silversmith Jean Baptist Rodriguez Elena Plis Sanjay Krishna 《Journal of Electronic Materials》2008,37(12):1764-1769
Mid-wavelength infrared (MWIR) p
+–n
−–n
+ avalanche photodiodes (APDs) were fabricated using two materials systems, one with mercury cadmium telluride (HgCdTe) on
a silicon (Si) substrate and the other with an indium arsenide/gallium antimonide (InAs/GaSb) strained layer superlattice
(SLS). Diode characteristics, avalanche characteristics, and excess noise factors were measured for both sets of devices.
Maximum zero-bias resistance times active area (R
0
A) of 3 × 106 Ω cm2 and 1.1 × 106 Ω cm2 and maximum multiplication gains of 1250 at −10 V and 1800 at −20 V were measured for the HgCdTe and the SLS, respectively,
at 77 K. Gains reduce to 200 in either case at 120 K. Excess noise factors were almost constant with increasing gain and were
measured in the range of 1 to 1.2. 相似文献
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Pau J.L. McClintock R. Bayram C. Minder K. Silversmith D. Razeghi M. 《Quantum Electronics, IEEE Journal of》2008,44(4):346-353
The authors report on the current-voltage (I-V) characteristic under forward biases obtained in low leakage, small size p-(In,Ga)N-GaN-n multiquantum well diodes. Under barrier illumination, the devices present a high optical response with capabilities to detect optical powers in the pW range without further amplification. This response is attributed to the screening of the internal electric fields. Recombination times of a few seconds are found to be associated to this mechanism. Moreover, a step-like feature is found in the I-V characteristic before the diode turn-on voltage. Our model proposes tunneling current through the multiquantum-well structure as responsible of this feature. Fast modulation of the tunneling effect under barrier illumination is used to evaluate the detection of low photon fluxes. 相似文献
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