Mapping the substrate-binding site of a human class mu glutathione transferase using nuclear magnetic resonance spectroscopy.

The substrate-binding site of a human muscle class mu glutathione transferase has been characterized using high-resolution nuclear magnetic resonance spectroscopy. Isotopic labeling has been used to simplify one-dimensional proton NMR spectra of the Tyr and His residues in the enzyme and two-dimensional carbon-proton spectra of the Ala and Met residues in the enzyme. The resonance lines from 8 of the 12 Tyr residues have been assigned using site-directed mutagenesis. Replacement of Tyr7 with Phe reduced the activity of the enzyme 100-fold. The proximity of His, Tyr, Ala, and Met residues to the active site has been determined using a nitroxide-labeled substrate analogue. This substrate analogue binds with high affinity (Keq = 10(6) M-1) to the enzyme and is a competitive inhibitor. None of the His residues are within 17 A of the active site. Three of the assigned Tyr residues are greater than 17 A from the active site. Quantitative measurement of paramagnetic line broadening of five additional Tyr residues places them within 13-17 A from the active site. Broadening of the Ala and Met resonance lines by the spin-labeled substrate indicates that three Ala residues are 9-16 A from the nitroxide, three Met residues are less than 9 A from the nitroxide, and two Met residues are 9-16 A from the nitroxide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gene expression and the evolution of phenotypic diversity in social wasps

Background  

Organisms are capable of developing different phenotypes by altering the genes they express. This phenotypic plasticity provides a means for species to respond effectively to environmental conditions. One of the most dramatic examples of phenotypic plasticity occurs in the highly social hymenopteran insects (ants, social bees, and social wasps), where distinct castes and sexes all arise from the same genes. To elucidate how variation in patterns of gene expression affects phenotypic variation, we conducted a study to simultaneously address the influence of developmental stage, sex, and caste on patterns of gene expression in Vespula wasps. Furthermore, we compared the patterns found in this species to those found in other taxa in order to investigate how variation in gene expression leads to phenotypic evolution.     

Quantitative assay of deoxyribonuclease activity after isoelectric focusing in polyacrylamide gels: pH control and effects of enzyme diffusion

A method for the quantitative assay of nuclease activity in crude cell lysates after isoelectric focusing (IEF) in polyacrylamide slab gels is described. After IEF, an agarose overlay gel containing DNA is placed on the IEF gel and the nuclease activity quantified by the loss of ethidium bromide fluorescence of the DNA. With this method a linear response was obtained for 1 to 10 ng of DNase I. Various methods of pH equilibration after IEF were also evaluated. The use of a high buffer concentration in the overlay gel is recommended to control the pH during the enzyme reaction. An analytical solution for the diffusion of enzymes from the IEF gel to the overlay gel is also presented and an equation that may be used to choose optimum times for transfer of the enzyme from the IEF gel to the overlay gel is given.     

Preliminary crystallographic study of C-reactive protein from Limulus polyphemus

Crystals of C-reactive protein from Limulus polyphemus have been grown both with and without calcium. The space group for the calcium-free crystals is I422 or I4(1)22, and the cell parameters are a = b = 173.33 (4) A, c = 98.81 (3) A. The crystals diffract to at least 2.8 A resolution and are suitable for detailed structural studies.     

Urinary C-type natriuretic peptide excretion: a potential novel biomarker for renal fibrosis during aging

Renal aging is characterized by structural changes in the kidney including fibrosis, which contributes to the increased risk of kidney and cardiac failure in the elderly. Studies involving healthy kidney donors demonstrated subclinical age-related nephropathy on renal biopsy that was not detected by standard diagnostic tests. Thus there is a high-priority need for novel noninvasive biomarkers to detect the presence of preclinical age-associated renal structural and functional changes. C-type natriuretic peptide (CNP) possesses renoprotective properties and is present in the kidney; however, its modulation during aging remains undefined. We assessed circulating and urinary CNP in a Fischer rat model of experimental aging and also determined renal structural and functional adaptations to the aging process. Histological and electron microscopic analysis demonstrated significant renal fibrosis, glomerular basement membrane thickening, and mesangial matrix expansion with aging. While plasma CNP levels progressively declined with aging, urinary CNP excretion increased, along with the ratio of urinary to plasma CNP, which preceded significant elevations in proteinuria and blood pressure. Also, CNP immunoreactivity was increased in the distal and proximal tubules in both the aging rat and aging human kidneys. Our findings provide evidence that urinary CNP and its ratio to plasma CNP may represent a novel biomarker for early age-mediated renal structural alterations, particularly fibrosis. Thus urinary CNP could potentially aid in identifying subjects with preclinical structural changes before the onset of symptoms and disease, allowing for the initiation of strategies designed to prevent the progression of chronic kidney disease particularly in the aging population.     

Aberrant energy-linked reactions in mitochondria isolated from the livers of rats infected with the liver fluke Fasciola hepatica.

The respiratory properties of mitochondria isolated from the livers of rats infected with the parasite Fasciola hepatica were examined. Oligomycin-sensitive ATPase activity was also examined during the acute stage (2-4 weeks post-infection). At 2,4 and 6 weeks post-infection, mitochondrial respiration in vitro (supported by site I and site II substrates) was completely uncoupled. Limited respiratory control had returned by 11 weeks post-infection, but complete recovery was not observed even at 21 weeks post-infection. At 4 weeks post-infection, uncoupled respiration (from all three energy-conserving sites) was also markedly attenuated (to the greatest extent with NADH-linked substrate). Except for pyruvate-supported respiration, this attenuation was not apparent at any other stage of the infection. The attenuation of pyruvate-supported respiration declined, but was still present, at 6 weeks post-infection. In addition to these perturbations in mitochondrial respiratory properties, mitochondrial ATPase activity at 4 weeks post-infection was insensitive to oligomycin, indicating a change in the structural integrity of the ATPase complex.