Histidine phosphorylation plays a key role in prokaryotic signaling and accounts for approximately 6% of the protein phosphorylation events in eukaryotics. Phosphohistidines generally act as intermediates in the transfer of phosphate groups from donor to acceptor molecules. Examples include the bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) and the histidine kinases found in two-component signal transduction pathways. The latter are utilized by bacteria and plants to sense and adapt to changing environmental conditions. Despite the importance of histidine phosphorylation in two-component signaling systems, relatively few proteins have so far been identified as containing phosphorylated histidine residues. This is largely due to the instability of phosphohistidines, which, unlike the phosphoesters formed by serine, threonine, and tyrosine, are labile and susceptible to acid hydrolysis. Nevertheless, it is possible to preserve and identify phosphorylated histidine residues in target proteins using appropriate sample preparation, affinity purification, and mass spectrometric techniques. This chapter provides a brief overview of such techniques, describes their use in confirming histidine phosphorylation of a known PTS protein (HPr), and suggests how this approach might be adapted for large-scale identification of histidinephosphorylated proteins in two-component systems.[27]identification of histidine phosphorylations 549
The paper is concerned with frictional study of a high-speed lubricated helical gear pair. The objectives were numerical evaluations of temperature and stress fields of the gear pair and the analysis of their frictional interaction in terms of the coefficient of friction. The problem was also investigated experimentally by temperature measurements at several points of a tooth. We developed an algorithm of numerical modeling based on an iterative scheme generating a sequence of approximate solutions to the temperature and stress fields till attainment of convergence of the numerically obtained and measured temperatures. Since the coefficient of friction significantly affected the frictional heat flux and thereby the temperature fields, it was used as a calibration parameter of the numerical model. Its magnitude was updated from an initial value until the one the process reached convergence with. The outcomes of the study include the temperature and stress fields, the magnitude of the coefficient of friction, and the frictional heat flux distribution.
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