Effects of introduced aspartic and glutamic acid residues on the P'1 substrate specificity, pH dependence and stability of carboxypeptidase Y

Carboxypeptidase Y is a serine carboxypeptidase isolated from Saccharomyces cerevisiae with a preference for C-terminal hydrophobic amino acid residues. In order to alter the inherent substrate specificity of CPD-Y into one for basic amino acid residues in P'1, we have introduced Asp and/or Glu residues at a number of selected positions within the S'1 binding site. The effects of these substitutions on the substrate specificity, pH dependence and protein stability have been evaluated. The results presented here demonstrate that it is possible to obtain significant changes in the substrate preference by introducing charged amino acids into the framework provided by an enzyme with a quite different specificity. The introduced acidic amino acid residues provide a marked pH dependence of the (kcat/Km)FA-A-R-OH/(kcat/Km)FA-A-L-OH ratio. The change in stability upon introduction of Asp/Glu residues can be correlated to the difference in the mean buried surface area between the substituted and the substituting amino acid. Thus, the effects of acidic amino acid residues on the protein stability depend upon whether the introduced amino acid protrudes from the solvent accessible surface as defined by the surrounding residues in the wild type enzyme or is submerged below.     

Estimation of deformation gradient and strain from cine-PC velocity data

Phase contrast magnetic resonance imaging (MRI) can provide in vivo myocardial velocity field measurements. These data allow densely spaced material points to be tracked throughout the whole heart cycle using, for example, the Fourier tracking algorithm. To process the tracking results for myocardial deformation and strain quantification, we developed a method that is based on fitting the tracking results to an appropriate local deformation model. We further analyzed the accuracy and precision of the method and provided performance predictions for several local models. In order to validate the method and the theoretical performance analysis, we conducted controlled computer simulations and a phantom study. The results agreed well with expectations. Human heart data were also acquired and analyzed, and provided encouraging results. At the signal-to-noise ratio (SNR) level and spatial resolution expected in clinical settings, the study predicts strain quantification accuracy and precision that may allow the technique to become a practical and powerful noninvasive approach for the study of cardiac function, although clinically acceptable data acquisition strategies for three-dimensional (3-D) data are still a challenge.     

Platelet-derived growth factor activates a mammalian Ste20 coupled mitogen-activated protein kinase in airway smooth muscle

Attempts to immunise sheep against natural infestations by Lucilia cuprina larvae have not been effective. Yet it is known that the larvae excrete the immunosuppressant ammonium bicarbonate. The effect of larval ammonium and nonionic ammonia on immunopathobiology was evaluated in 12 infested sheep. The concentration of ammonium in veins draining infested sites was measured in another group of four sheep. Mean jugular unionized ammonia concentration increased 3.5 to 5.6 times above pre-infested control levels. Mean venous ammonium concentrations draining infested sites were 13 times higher than pre-infested jugular or carotid levels. Increases in jugular ammonia concentrations correlated with increased number of larvae, area of infestation, earlier death, neutropenia, eosinopenia, lymphocytopenia, large declines in serum globulins and zinc, and large rises in toxic neutrophils. The high concentrations of toxic unionized ammonia in blood directly permanently damaged neutrophils and lymphocytes and depressed serum globulin production. The results show that the ammonium from the excreta of larvae of L. cuprina may be highly immunosuppressive.     

Comfort limits for asymmetric thermal radiation

Groups of 32 and 16 subjects of both sexes were exposed in an environmental chamber to radiant asymmetry caused by a cool wall, a warm wall, and a cool ceiling. Each subject was tested individually while seated and clothed at 0.6 clo. During each 3.5-hour experiment the subject was exposed to six radiant temperature asymmetries. He was asked whether and where he experienced any local cool or warm sensation, and whether it was felt to be uncomfortable. During the entire experiment he was kept thermally neutral by changing the air temperature according to his wishes.For cool walls, warm walls, and cool ceilings curves have been established showing the percentage of dissatisfied subjects as a function of the radiant asymmetry. Radiant asymmetry at a warm wall caused less discomfort than a cool wall. A cool ceiling caused less discomfort than a warm ceiling. Accepting that 5% of the subjects may feel uncomfortable. a radiant temperature asymmetry of 10°C is allowable at a cool wall, 23°C at a warm wall, and 14°C under a cool ceiling. A previous study showed that 4°C is allowable under a warm ceiling. Radiant asymmetry had no significant impact on the operative temperatures preferred by the subjects. No significant differences were observed between the responses of men and women exposed to radiant asymmetry.     

Power management in networked devices

Networks are one of the most significant developments in computing and a hallmark of modern society. However, along with increasing efficiency and productivity, both at home and in the workplace, networks have costs. One cost is the additional energy that electronic devices consume when attached to networks. Power management, a standard feature of modern PCs, was primarily developed to increase battery lifetime in laptop PCs, which historically were not network-connected when using battery power. Today, however, many laptops are connected to a network - typically a Wi-Fi network - as are the majority of desktop computers. Three key drivers of energy use are induced consumption by devices prevented by network connections from entering low-power states, increasing link data rates that inherently consume more energy for the network interfaces, and proliferation of network-connected displays that actively update and display data when no one is present.     

Reflex jaw motions and jaw stiffness pertaining to whiplash injury of the neck

Because a so-called mandibular whiplash injury requires the absence of short-latency jaw-closing reflexes in order to explain the postulated mechanism of injury (excessive jaw opening); the authors studied the presence and absence and more importantly, the kinematics (duration, displacement, velocity, acceleration) of monosynaptic and possibly, polysynaptic myotatic (stretch) reflexes in the jaw elevator muscles. In six healthy adults jaw jerk maneuvers were elicited through a brisk tap on the chin, and surface electromyography identified elevator reflexes while translational electrognathography identified the kinematics of the reflexes. The maneuvers were done while maintaining the rest position (3% MVC) and moderate clenching of the teeth (30% MVC). Electromyography was also used to identify phasic elevator excitations during a passive brisk neck extension maneuver. A sudden and unexpected elongation of the jaw elevators released autogenic reflex responses that, in conjunction with augmented tissue elasticity (stiffness), elevated the mandible into centric occlusion within approximately 150 milliseconds. In 86% of trials, the responses occurred regardless of the prevailing resting and clenching contractile activities. There was no evidence of a depressor force that consistently would and could anchor the mandible in a position of extreme or moderate depression, the theoretical linchpin of the mandibular whiplash injury. It was concluded that the mandibular locomotor system is very efficient in maintaining the rest and intercuspal positions of the mandible. This study found no evidence corroborating the mechanism claimed to release a so-called mandibular whiplash injury.     

Hand, space and attentional asymmetries in goal-directed manual aiming

Two experiments were conducted to explore the interaction of the two cerebral hemispheres in motor control, by examining hand, space and attentional asymmetries in goal-directed aiming. In Experiment 1, right-handed subjects moved to targets more quickly with their right hand than their left hand. In addition, each hand was faster when moving in its own hemispace. Although in a control condition, movements were initiated more quickly with the left hand, visual distractors disrupted left hand performance more than right hand performance. For contralateral aiming, ipsilateral distractors caused the greatest interference. In Experiment 2, when targets and distractors were all presented at the midline, a right hand advantage was found for movement time along with a left hand advantage for reaction time, independent of target and distractor location. Our findings are discussed in terms of a right hemisphere role in movement preparation and the allocation of attention in space, and greater left hemisphere involvement in movement execution.