A comparison of functional and structural consequences of the tyrosine B10 and glutamine E7 motifs in two invertebrate hemoglobins (Ascaris suum and Lucina pectinata)

The architecture of the distal heme pocket in hemoglobins and myoglobins can play an important role in controlling ligand binding dynamics. The size and polarity of the residues occupying the distal pocket may contribute steric and dielectric effects. In vertebrate systems, the distal pocket typically contains a "distal" histidine at position E7 and a leucine at position B10. There are several invertebrate organisms that have hemoglobins or myoglobins that display a pattern in which residues E7 and B10 are a glutamine and tyrosine, respectively. These proteins often have very high oxygen affinities stemming from very slow ligand off rates. In this study, two such hemoglobins, one from the nematode Ascaris suum and the other from the sulfide-fixing clam Lucina pectinata, are compared with respect to conformational and functional properties. Ultraviolet resonance Raman spectroscopy and visible resonance Raman spectroscopy are used to probe, respectively, the ligand-dependent hydrogen bonding pattern of the tyrosine residues and the proximal heme pocket interactions. Fourier transform infrared absorption spectroscopy is used to probe the dielectric properties of the distal heme pocket through the stretching frequency of carbon monoxide bound to the heme. Functionality is probed through the geminate rebinding of both CO and O2. The findings reveal two very different patterns indicative of two different mechanisms for achieving low oxygen off rates. In Hb Ascaris, a hydrogen bonding network that includes the E7 Gln, B10 Tyr, and oxygen bound to the heme results in a tight cage for the oxygen. Dissociation of the O2 requires a large amplitude conformational fluctuation that results both in a spontaneous dissociation of the oxygen through the loss of hydrogen bond stabilization and in an enhanced probability for ligand escape though the transient disruption and opening of the tight distal cage. In the case of the Hb from Lucina, there is no evidence for a tight cage. Instead the data support a model in which the hydrogen bonding network is far more tenuous and the equilibrium state of distal pocket is far more open and accessible than is the case in Ascaris. The results explain why Hb Ascaris has one of the highest oxygen affinities known (P50 approximately 10(-)3 Torr) while Hb Lucina II has an oxygen affinity comparable to that of Mb (P50 = 0.13 Torr) even though both of these Hbs contain the B10 Tyr and E7 Gln motif and display very low oxygen off rates. The roles of water and proximal strain are discussed.     

On the use of O2 spin-rotation lines for elevation angle calibration of atmospheric thermal emission spectra

The magnetic dipole-allowed spin-rotation lines of O₂ potentially can be used for pointing calibration and confirmation of float altitude for far infrared spectra of the stratosphere obtained from balloon platforms. We demonstrate that current deficiencies in the spectroscopic database, particularly the air pressure-broadening coefficients, severely limit the capability of deriving useful pointing calibrations, and that precise pressure-broadening measurements for the transitions actually used in calibration are needed to improve this capability.     

Children whose mothers are HIV infected: Who resides in the home and is there a relationship to child psychosocial adjustment?

This study examined who resides in the home when a mother is HIV infected and whether this relates to child psychosocial adjustment. Participants were 249 inner-city African American women, 40% of whom were HIV infected, and their 6- to 11-year-old children. HIV-infected women in the symptomatic–AIDS stage were more likely than noninfected mothers to have more adults, particularly a grandmother or aunt of the child, and more adults per child residing in the home. Only the ratio of adults-to-children in the home was related to child adjustment, and this occurred primarily when mothers were in the symptomatic–AIDS stage of infection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How to develop better system requirements

It is not easy to get a complete set of design requirements. The authors discuss a way to help draw out users' needs. They consider how scenarios can help you identify and analyze requirements by detecting missing requirements and encouraging a discussion and review of the system's dynamic behavior     

A Time-Sharing Instrument for Direct Readout of Oxidation-Reduction States in Intracellular Compartments of Cardiac Tissue

Internal fluorochromes and chromophores afford the possibility of a continuous, nondestructive readout of biochemical information from complex systems such as intact organs. An instrument has been constructed which allows simultaneous observation of fluorescence emission from reduced pyridine nucleotides [NAD(P)H] and certain oxidized flavoproteins together with dual wavelength absorption measurements of cytochrome b. The instrument is applied to a preparation of perfused frog heart. The kinetic responses of the three parameters to oxygen, nitrogen, and 2-mM amytal are observed. Flavoprotein and cytochrome b show a delayed reduction in response to a transition from O2 to N2.NAD(P)H shows an early small reduction which can be attributed to the interaction of a cytoplasmic pool with oxidases located in peroxisomes and the endoplasmic reticulum. Addition of amytal to the oxygenated perfusate produces a small additional oxidation of cytochrome b.     

Waveform generation by enzymatic oscillators

The control of cell chemistry is being investigated through a multipronged approach combining the techniques of physics, chemistry, and biology with the development of electronic instrumentation and the application of analog and digital computers. An example of such metabolic control phenomena is provided by biological oscillators involving enzymatic reactions. These oscillators, which may exist in nearly every kind of cell and even in several forms in a single cell, reveal basic instabilities in biochemical reactions and metabolic control that may be of significance to health and disease. In addition, the high-frequency oscillations observed in simple enzyme systems may be models for the longer-period rhythms that regulate the activities of nearly all biological systems.     

Radiolytic modification of acidic amino acid residues in peptides: probes for examining protein-protein interactions

Hydroxyl radical-mediated footprinting coupled with mass spectroscopic analysis is a new technique for mapping protein surfaces, identifying structural changes modulated by protein-ligand binding, and mapping protein-ligand interfaces in solution. In this study, we examine the radiolytic oxidation of aspartic and glutamic acid residues to probe their potential use as structural probes in footprinting experiments. Model peptides containing Asp or Glu were irradiated using white light from a synchrotron X-ray source or a cesium-137 gamma-ray source. The radiolysis products were characterized by electrospray mass spectrometry including tandem mass spectrometry. Both Asp and Glu are susceptible to radiolytic oxidization by gamma-rays or synchrotron X-rays. Radiolysis results primarily in the oxidative decarboxylation of the side chain carboxyl group and formation of an aldehyde group at the carbon next to the original carboxyl group, giving rise to a characteristic product with a -30 Da mass change. A similar oxidative decarboxylation also takes place for amino acids with C-terminal carboxyl groups. The methylene groups in the Asp and Glu side chains also undergo oxygen addition forming ketone or alcohol groups with mass changes of +14 and +16 Da, respectively. Characterizing the oxidation reactions of these two acidic residues extends the number of useful side chain probes for hydroxyl radical-mediated protein footprinting from 10 (Cys, Met, Trp, Tyr, Phe, Arg, Leu, Pro, His, Lys) to 12 amino acid residues, thus enhancing our ability to map protein surface structure and in combination with previously identified basic amino acid probes can be used to examine molecular details of protein-protein interactions that are driven by electrostatics.     

Effects of sample temperature in femtosecond single-pulse laser-induced breakdown spectroscopy

As much as tenfold atomic emission enhancements have been observed in experiments combining nanosecond (ns) and femtosecond (fs) laser pulses in an orthogonal dual-pulse configuration for laser-induced breakdown spectroscopy (ns-fs orthogonal dual-pulse LIBS). In the examination of one of several potential sources of these atomic emission enhancements (sample heating by a ns air spark), minor reductions in atomic emission and as much as 15-fold improvements in mass removal have been observed for fs single-pulse LIBS of heated brass and aluminum samples. These results suggest that, although material removal with a high-powered, ultrashort fs pulse is temperature dependent, sample heating by the ns air spark is not the source of the atomic emission enhancements observed in ns-fs orthogonal dual-pulse LIBS.