Yingchun Li

Phosphotriesterase (PTE) from Pseudomonas diminuta is a zinc metalloenzyme that hydrolyzes a variety of organophosphorus compounds. The kinetic parameters of Zn/Zn PTE, Cd/Cd PTE, and a mixed-metal Zn/Cd hybrid PTE were obtained with a variety of substrates to determine the role of each metal ion in binding and catalysis. pH-rate profiles for the hydrolysis of diethyl p-nitrophenyl phosphate (I) and diethyl p-chlorophenyl phosphate (II) demonstrated that the ionization of a single group in the pH range of 5-10 was critical for substrate turnover. The pK(a) values determined from the kinetic assays were dependent on the identity of the metal ion that occupied the alpha site within the binuclear metal center. These results suggest that the hydrolytic nucleophile is activated as a hydroxide via the ionization of a water molecule attached to the alpha-metal ion. The kinetic constants for the hydrolysis of II and diethyl p-chlorophenyl thiophosphate (IV) were determined for the metal substituted forms of PTE. The kinetic constants for IV were greater than those for II. The inverse thio effect is consistent with the polarization of the phosphoryl oxygen/sulfur bond via a direct ligation to the metal center. The rate enhancement is greater when Cd(2+) occupies the beta-metal-ion position. A series of alanine and asparagine mutations were used to characterize the catalytic roles of Asp233, His254, and Asp301. Mutations to either Asp233 or His254 resulted in an enhanced rate of hydrolysis for the sluggish substrate, diethyl p-chlorophenyl phosphate, and a decrease in the kinetic constants for paraoxon (I). These results are consistent with the existence of a proton relay from Asp301 to His254 to Asp233 that is used to ferry protons away from the active site with substrates that do not require activation of the leaving group phenol. A mechanism for the hydrolysis of organophosphates by the bacterial PTE has been proposed.

In satellite to mobile communications, there is generally, in addition to the diffuse multipath component, a strong line-of-sight (LOS) component present. The spectral and statistical properties of both components are influenced by shadowing caused by obstacles such as trees, houses, or small buildings. In this paper, an analytical model for a land mobile satellite channel is analyzed that takes into consideration various kinds of shadowing situations. For the LOS component, it is assumed that, first, the received frequency shows a Doppler shift. Second, the amplitude variations coincide with a lognormal distribution. Moreover, it is also assumed that shadowing influences the diffuse scattered component, with the consequence that its Doppler power spectrum gets an asymmetrical shape. The resulting spectral and statistical properties of the analytical model are investigated. Exact solutions for the probability density function (pdf) of the amplitude and phase are given, and approximative solutions for the level-crossing rate (LCR) and average duration of fades (ADFs) are derived. Finally, an efficient deterministic simulation model is presented that enables the implementation of the proposed analytical model on a digital computer.

We analyzed 18 high-quality waveform doublets with time separations of up to 35 years in the South Sandwich Islands region, for which the seismic signals have traversed the inner core as PKP(DF). The doublets show a consistent temporal change of travel times at up to 58 stations in and near Alaska, and they show a dissimilarity of PKP(DF) coda. Using waveform doublets avoids artifacts of earthquake mislocations and contamination from small-scale heterogeneities. Our results confirm that Earth's inner core is rotating faster than the mantle and crust at about 0.3 degrees to 0.5 degrees per year.

OBJECTIVES: Early placement of transjugular intrahepatic portosystemic shunt (TIPS) has been shown to improve survival in high-risk patients (Child-Pugh B plus active bleeding at endoscopy or Child-Pugh C 10-13) with cirrhosis and acute variceal bleeding (AVB). However, early TIPS criteria may overestimate the mortality risk in a significant proportion of patients, and the survival benefit conferred by early TIPS in such patients has been questioned. Alternative criteria have been proposed to refine the criteria used to identify candidates for early TIPS. Nevertheless, the true survival benefit provided (or not) by early TIPS compared with standard treatment in the different risk categories has not been investigated in specifically designed comparative studies. DESIGN: We collected data on 1425 consecutive patients with cirrhosis and AVB who were admitted to 12 university hospitals in China between December 2010 and June 2016. Of these, 206 patients received early TIPS, and 1219 patients received standard treatment. The Fine and Gray competing risk regression model was used to compare the outcomes between the two groups that were stratified based on the currently available risk stratification systems after adjusting for liver disease severity and other potential confounders. RESULTS: Overall, early TIPS was associated with an 80% relative risk reduction (RRR) in mortality at 6 weeks (adjusted HR=0.20; 95% CI: 0.10 to 044; p<0.001) and 51% RRR at 1 year (adjusted HR=0.49, 95% CI: 0.32 to 0.73; p<0.001) compared with standard treatment. In stratification analyses, the RRRs in mortality did not significantly differ among the risk categories. However, the absolute risk reductions (ARRs) of mortality were more pronounced in high-risk patients. The ARRs at 6 weeks were -2.1%, -10.2% and -32.4% in Model for End-stage Liver Disease (MELD) ≤11, 12-18 and ≥19 patients and were -1.5%, -9.1% and -23.2% in Child-Pugh A, B and C patients, respectively (interaction tests, p<0.001 for both criteria). The ARRs for mortality at 1 year were -1.7%, -5.4% and -32.7% in MELD ≤11, 12-18 and ≥19 patients, respectively, and -3.6%, -5.2% and -20.3% in Child-Pugh A, B and C patients, respectively (interaction tests, p<0.001 for both criteria). After adjusting for liver disease severity and other potential confounders, a survival benefit was observed in MELD ≥19 or Child-Pugh C patients but not in MELD ≤11 or Child-Pugh A patients. In MELD 12-18 patients, a survival benefit was observed within 6 weeks but not at 1 year. In Child-Pugh B patients, a survival benefit was observed in those with active bleeding but not those without active bleeding. However, the evaluation of active bleeding was associated with a high interobserver variability. Furthermore, early TIPS was associated with a significantly reduced incidence of failure to control bleeding or rebleeding and new or worsening ascites, without increasing the risk of overt hepatic encephalopathy. CONCLUSIONS: Early TIPS was associated with improved survival in patients with MELD ≥19 or Child-Pugh C cirrhosis but not in patients with MELD ≤11 or Child-Pugh A cirrhosis. For MELD 12-18 or Child-Pugh B patients, future studies addressing optimal selection criteria for early TIPS remain highly warranted.