High-resolution crystal structures of delta5-3-ketosteroid isomerase with and without a reaction intermediate analogue

Bacterial Delta5-3-ketosteroid isomerase (KSI) catalyzes a stereospecific isomerization of steroid substrates at an extremely fast rate, overcoming a large disparity of pKa values between a catalytic residue and its target. The crystal structures of KSI from Pseudomonas putida and of the enzyme in complex with equilenin, an analogue of the reaction intermediate, have been determined at 1.9 and 2.5 A resolution, respectively. The structures reveal that the side chains of Tyr14 and Asp99 (a newly identified catalytic residue) form hydrogen bonds directly with the oxyanion of the bound inhibitor in a completely apolar milieu of the active site. No water molecule is found at the active site, and the access of bulk solvent is blocked by a layer of apolar residues. Asp99 is surrounded by six apolar residues, and consequently, its pKa appears to be elevated as high as 9.5 to be consistent with early studies. No interaction was found between the bound inhibitor and the residue 101 (phenylalanine in Pseudomonas testosteroni and methionine in P. putida KSI) which was suggested to contribute significantly to the rate enhancement based on mutational analysis. This observation excludes the residue 101 as a potential catalytic residue and requires that the rate enhancement should be explained solely by Tyr14 and Asp99. Kinetic analyses of Y14F and D99L mutant enzymes demonstrate that Tyr14 contributes much more significantly to the rate enhancement than Asp99. Previous studies and the structural analysis strongly suggest that the low-barrier hydrogen bond of Tyr14 (>7.1 kcal/mol), along with a moderate strength hydrogen bond of Asp99 ( approximately 4 kcal/mol), accounts for the required energy of 11 kcal/mol for the transition-state stabilization.     

Glossolalia as learned behavior: An experimental demonstration.

60 18–44 yr old undergraduates listened to a 60-sec sample of glossolalia (defined to them as pseudolanguage) and then attempted to produce glossolalia on a 30-sec baseline trial. Afterward, half of the Ss received 2 training sessions that included audio- and videotaped samples of glossolalia interspersed with opportunities to practice glossolalia. Also, live modeling of glossolalia, direct instruction, and encouragement were provided by an experimenter. Both the trained Ss and untreated controls attempted to produce glossolalia on a 30-sec posttest trial. About 20% of Ss exhibited fluent glossolalia on the baseline trial, and training significantly enhanced fluency. 70% of trained Ss spoke fluent glossolalia on the posttest. Findings are more consistent with social learning than with altered state conceptions of glossolalia. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Net generation or Digital Natives: Is there a distinct new generation entering university?

This article reports key findings from the first phase of a research project investigating Net generation age students as they encounter e-learning at five universities in England. We take a critical view of the idea of a distinct generation which has been described using various terms including Net generation and Digital Natives and explore age related differences amongst first year university students. The article draws on evidence from a survey of first year undergraduates studying a range of pure and applied subjects. Overall we found a complex picture amongst first-year students with the sample population appearing to be a collection of minorities. These included a small minority that made little use of some technologies and larger minorities that made extensive use of new technologies. Often the use of new technology was in ways that did not fully correspond with the expectations that arise from the Net generation and Digital Natives theses. The article concludes that whilst there are strong age related variations amongst the sample it is far to simplistic to describe young first-year students born after 1983 as a single generation. The authors find that the generation is not homogenous in its use and appreciation of new technologies and that there are significant variations amongst students that lie within the Net generation age band.     

Low-frequency suppression of auditory nerve responses to characteristic frequency tones

The effects of low-frequency (50, 100, 200 and 400 Hz) 'suppressor' tones on responses to moderate-level characteristic frequency (CF) tones were measured in chinchilla auditory nerve fibers. Two-tone interactions were evident at suppressor intensities of 70-100 dB SPL. In this range, the average response rate decreased as a function of increasing suppressor level and the instantaneous response rate was modulated periodically. At suppression threshold, the phase of suppression typically coincided with basilar membrane displacement toward scala tympani, regardless of CF. At higher suppressor levels, two suppression maxima coexisted, synchronous with peak basilar membrane displacement toward scala tympani and scala vestibuli. Modulation and rate-suppression thresholds did not vary as a function of spontaneous activity and were only minimally correlated with fiber sensitivity. Except for fibers with CF < 1 kHz, modulation and rate-suppression thresholds were lower than rate and phase-locking thresholds for the suppressor tones presented alone. In the case of high-CF fibers with low spontaneous activity, excitation thresholds could exceed suppression thresholds by more than 30 dB. The strength of modulation decreased systematically with increasing suppressor frequency. For a given suppressor frequency, modulation was strongest in high-CF fibers and weakest in low-CF fibers. The present findings strongly support the notion that low-frequency suppression in auditory nerve fibers largely reflects an underlying basilar membrane phenomenon closely related to compressive non-linearity.     

Sj?gren''s syndrome in patients with newly diagnosed untreated non-Hodgkin''s lymphoma

A prfA gene encoding polypeptide release factor RF1 was cloned from Thermus thermophilus. T thermophilus RF1 shares 68% homology with Escherichia coli RF1, and its overproduction reduced readthrough translation of UAG, not of UGA, in the lacZ gene. Rapid purification of T thermophilus RF1 was achieved by T7-RNA polymerase driven overexpression of T thermophilus RF1 protein with a C-terminal histidine tag.     

Information seeking in social context: structural influences andreceipt of information benefits

Research in the information processing, situated learning and social network traditions has consistently demonstrated the importance of social networks for acquiring information. However, we know little about how organizational relationships established by a relative position in a formal structure or social relationships established by interpersonal processes influence who is sought out for various kinds of information. Prior research suggests that people often receive some combination of five benefits when seeking information from other people: (1) solutions; (2) meta-knowledge (pointers to databases or people); (3) problem reformulation; (4) validation of plans or solutions; and (5) legitimation from contact with a respected person. This research builds on that work by assessing the influence of organizational and social structures (such as similarity of job function, hierarchy, task interdependence, physical proximity, influence, trust, friendship and gender) on receipt of these benefits from other people in a physically distributed organization. Task interdependence is the strongest and most consistent predictor of information seeking. However, social relations also affect the receipt of informational benefits, especially as they become more representational and affective. Implications are suggested for the study of social capital, computer-mediated communication and organizational learning     

The Effect of Gate-Bias Stress and Temperature on the Performance of ZnO Thin-Film Transistors

The stability of ZnO thin-film transistors is investigated by using gate-bias stress. It is found that the application of positive and negative stress results in the device transfer characteristics shifting in positive and negative directions, respectively. It is postulated that this device instability is a consequence of charge trapping at or near the channel/insulator interface. In addition, there is a degradation of subthreshold behavior and channel mobility, which is suggested to result from the defect-state creation within the ZnO layer. The effect of elevated temperature stress shows a predominance of interface-state creation in comparison to trapping under gate-bias stress. Device instability appears to be a consequence of the charging and discharging of preexisting trap states at the interface and in the channel region of the devices. All stressed devices recover their original characteristics after a short period at room temperature without the need for any thermal or bias annealing.