Orotate phosphoribosyltransferase from Thermus thermophilus: overexpression in Escherichia coli, purification and characterization

Orotate phosphoribosyltransferase (OPRTase, EC2.4.2.10) plays a role in de novo synthesis of pyrimidine nucleotide and transfers orotate to 5-phosphoribosyl-1-pyrophosphate (PRPP) to form orotidine-5'-monophosphate (OMP). To obtain heat-stable OPRTase and to elucidate the mechanism of heat stability, this enzyme from Thermus thermophilus was expressed in Escherichia coli and purified. The pyrE gene of T. thermophilus which encodes OPRTase, contains an open reading frame of 549 base pairs with 69% G+C content. Since this gene expressed itself inefficiently in E. coli, the 5' and 3' ends of the coding regions were replaced with synonymous codons which contain more A+T and corresponds to major codons for E. coli. Introduction of the modified gene fragments into a plasmid having a tac promoter resulted in production of a polypeptide of molecular weight (M(r)) 20,000 in the presence of isopropyl-beta-D-thiogalactopyranoside (IPTG) in E. coli. This protein represented as much as 16% of the bacterial total protein and showed the OPRTase activity. Three purification steps, consisting of heat treatment at 65 degrees C, 40% ammonium sulfate fractionation, and KCl gradient elution from DEAE-Sephadex A-50, resulted in highly purified single polypeptide. The optimum activity of the purified OPRTase was observed at 150 mM KCl, pH 9.0, 75-80 degrees C, and in the presence of 100 microM PRPP. The activation energy of this enzyme reaction was 20.3 kJ/mol. The Km of this enzyme for orotate as a substrate was 75 microM and the maximum specific activity was 300 units/mg protein under the optimum conditions. The purified OPRTase was stable for 20 min at 85 degrees C.

Systemic and cellular calcium metabolism and hypertension

The calcium status of humans with essential hypertension and genetic animal models of hypertension is characterized by low serum ionized calcium concentration, increased urinary calcium excretion, and increased parathyroid hormone (PTH) concentration. Calcitriol metabolism and bone mineralization are also altered in hypertension. These alterations in systemic calcium metabolism may be linked to factors responsible for the elevated blood pressure. Cytosolic free calcium tends to be increased in most cells that have been studied from hypertensive humans and animals. Changes in cellular calcium metabolism may be partly mediated by calcium-regulating hormones that tend to be elevated in essential hypertension such as PTH and calcitriol. Administration of supplemental dietary calcium tends to suppress PTH, calcitriol, and intracellular free calcium. Further research is need concerning the observed association among systemic markers of calcium metabolism, cellular calcium metabolism, and arterial blood pressure regulation.

Dietary salt decreases cytosolic calcium in platelets from Dahl salt-sensitive rats

To determine whether abnormal cellular Ca2+ handling is involved in salt-induced hypertension of Dahl salt-sensitive rats (DS), we investigated Ca2+ handling in fura 2-loaded platelets of DS and Dahl salt-resistant rats (DR) fed a high-NaCl (8%) or a low-NacL (0.3%) diet for 4 wk from 5 wk of age. At 5 wk of age, blood pressure, resting cytosolic Ca2+ concentration ([Ca2+]i), the thrombin-evoked increase in [Ca2+]i and the size of internal Ca2+ stores of DS were comparable with those of DR. After 4 wk on the diets, resting [Ca2+]i of DS on high-NaCl diet was lower than that of DS on low-NaCl diet, and there was no effect of high salt intake on resting [Ca2+]i in DR. In DS, high salt intake attenuated the [Ca2+]i response to thrombin in the presence of external Ca2+. In contrast, the [Ca2+]i response to thrombin in the absence of external Ca2+ was enhanced by high salt intake in DS. The size of internal Ca2+ stores was increased by high salt intake in DS but not in DR. These data suggest that it is not obligatory for hypertension to be accompanied by an increase in platelet [Ca2+]i.

Crystallization and preliminary X-ray studies of isocitrate dehydrogenase from Thermus thermophilus HB8

Isocitrate dehydrogenase from the thermophilic bacterium, Thermus thermophilus HB8, was crystallized by the vapor diffusion hanging drop method with polyethylene glycol 6000 as the precipitant. Pillar-like crystals of about 0.6 x 0.6 x 0.3 mm3 were obtained. Analysis of a series of oscillation photographs indicated that the orthorhombic crystals belonged to the I222 or I2(1)2(1)2(1) space group with unit cell dimensions of a = 100.1 A, b = 150.4 A, and c = 87.4 A. Intensity data were collected up to 2.5 A resolution.

Ligand-induced changes in the conformation of 3-isopropylmalate dehydrogenase from Thermus thermophilus

The structures of 3-isopropylmalate dehydrogenase (IPMDH) from Thermus thermophilus in complexes with its substrate, cofactor, and a cofactor analog were investigated by X-ray diffraction in a crystalline state and by small-angle X-ray scattering (SAXS) in solution. The structures at 2.8 A resolution of the complexes with the substrate, 3-isopropylmalate (IPM), and with an analog of NAD, ADP-ribose, were both very close to the structure of the free enzyme, which adopts an open conformation. However, the binding of a ligand induced a small conformational change near the binding site. This result contrasts with results for NADP(+)-bound and isocitrate-bound isocitrate dehydrogenase (ICDH) from Escherichia coli, which adopts a closed conformation. The SAXS analysis in solution clearly showed that IPMDH without a ligand adopts two distinct intermediate conformations, between the open and closed states, upon binding of NADH and IPM respectively, and adopts a fully closed conformation when in a ternary complex with NADH and IPM together.

Angioscopic detection of residual pulmonary thrombi in the differential diagnosis of pulmonary embolism

Definite diagnosis of pulmonary embolism (PE) by conventional methods such as angiography is frequently difficult. If residual thromboemboli incorporated into the pulmonary arterial wall or in the distal small segments are visible, differential diagnosis of PE versus primary pulmonary hypertension (PPH) can be made without open-chest pulmonary biopsy. Six patients suspected of having acute PE, 6 suspected of having chronic PE, and 4 with PPH diagnosed by pulmonary biopsy underwent percutaneous pulmonary angioscopy. In patients suspected of having PE, globular and mural thromboemboli were detected by both angioscopy and angiography in 4 and 1 patients, respectively. By angioscopy, emboli incorporated into the arterial wall were detected in 7 and microemboli obstructing the distal small segments were detected in 6. However, these emboli were detected by angiography in none. In patients with PPH, no embolus was detected by angioscopy and angiography. Angioscopically, however, stenoses were observed in the distal small segments in all patients. The results indicate that residual pulmonary thromboemboli in PE and stenoses of distal pulmonary arteries in PPH are detectable by percutaneous angioscopy, and therefore this method is feasible for differential diagnosis of PE.

Purification and characterization of 3-isopropylmalate dehydrogenase from a thermoacidophilic archaebacterium Sulfolobus sp. strain 7

3-Isopropylmalate dehydrogenase was purified (about 2000-fold) to homogeneity for the first time from an archaebacterium, Sulfolobus sp. strain 7. The enzyme showed an apparent molecular mass of about 110 kDa by gel filtration and a single 36-kDa polypeptide band on SDS-PAGE, suggesting tri- or tetrameric structure. The pI value was 6.9. The N-terminal amino acid sequence was similar to enzymes from other sources. The enzyme activity was greatly stimulated by the presence of Mn2+, Cd2+, Mg2+, or Co2+. In contrast to 3-isopropylmalate dehydrogenase from other sources, monovalent cations such as K+ and Na+ were neither essential for activity nor stability of the protein. The enzyme was extraordinarily thermostable.

Morphological variation of new Thermoplasma acidophilum isolates from Japanese hot springs

We isolated 12 strains of Thermoplasma acidophilum from hot springs in Hakone, Japan. T. acidophilum strains showed morphological variation in the crystal-like structure in the cell and the fibrous structure on the cell surface. Two strains tested were sensitive to novobiocin. However, a novobiocin-resistant mutant was obtained by spontaneous mutation.

Effect of the transmembrane gradient of magnesium and sodium on the regulation of cytosolic free magnesium concentration in human platelets

1. To clarify the mechanism by which cytosolic free Mg2+ concentrations ([Mg2+]i) are regulated in human platelets, we investigated platelet membrane permeability to Mg2+ by altering extracellular Mg2+ concentrations, and tested the existence of a Na(+)-Mg2+ exchanger by manipulating the transmembrane Na+ gradient. 2. Platelet [Mg2+]i was 421 +/- 52 mumol/l in healthy men. [Mg2+]i remained constant during a 120 min exposure to nominally zero (low) or 5 mmol/l (high) external Mg2+ concentrations. 3. Preincubation of platelets with 10(-4) mol/l ouabain effectively decreased the transmembrane Na+ gradient. The ouabain-induced increase in [Mg2+]i was statistically significant after 30 min of exposure (14.6 +/- 2.0%) and reached 24.6 +/- 4.5% after 60 min. Similarly, the replacement of extracellular Na+ with N-methyl-D-glucamine significantly increased [Mg2+]i by 48.5 +/- 3.9% and 78.8 +/- 12.5%, respectively. 4. These results suggest that [Mg2+]i is well controlled in the presence of large transmembrane Mg2+ concentration gradients, and a Na(+)-Mg2+ exchanger may be involved in the regulation of [Mg2+]i in human platelets.

The crystal structure of thermostable mutants of chimeric 3-isopropylmalate dehydrogenase, 2T2M6T

A chimeric 3-isopropylmalate dehydrogenase (IPMDH), 2T2M6T, was produced by replacing the amino acid sequences of the Thermus thermophilus enzyme with those of the Bacillus subtilis enzyme from residues 75 to 113. Decreased thermostability of the chimeric enzyme was recovered by either evolutionary engineering (I93L) or site-directed mutagenesis (S82R). The 3-D structures of the mutants have been determined by X-ray diffraction at 2.1 A resolution. Although S82R was refined routinely, I93L required the preliminary rigid-body refinement of each domain. The R-factors were reduced to 0.18 for both mutants. Removal of the unfavorable torsion angle at isoleucine 93 may have made I93L more thermostable than 2T2M6T. In the case of S82R, the replaced arginine residue contributed to the extra hydrogen bond with water molecules. The large replaced residue decreased the entropy of the solvent, which may have caused the improvement in enzyme thermostability. Denaturation by heating may be interpreted from these structural results.

Prediction of acute coronary syndromes by percutaneous coronary angioscopy in patients with stable angina

To pinpoint the link between plaque characteristics and acute coronary syndromes, we performed a 12-month prospective follow-up study in 157 patients with stable angina pectoris in whom regular coronary plaques were observed by percutaneous coronary angioscopy. Acute coronary syndromes occurred more frequently in patients with yellow plaque than in those with white plaques (11 of 39 vs 4 of 118; p = 0.00021). Moreover, the syndromes occurred more frequently in patients with glistening yellow plaques than in those with nonglistening yellow plaques (9 of 13 vs 2 of 26; p = 0.00026). Thrombus arising from the ruptured identical plaques was confirmed by angioscopy as the culprit lesion of the syndromes. The results indicate that acute coronary syndromes occur frequently and in a short time in patients with glistening yellow plaques and that angioscopy but not angiography is feasible for prediction of the syndromes.

Specific antibody patterns of Wistar rats inoculated with third stage larvae of Anisakis simplex

Levels of excretory-secretory (ES)-specific antibody were measured in Wistar rats inoculated with 1, 5, or 20 third stage larvae (L3) of Anisakis simplex. Primary inoculation induced ES-specific IgM and IgG titers, paralleling inoculum size. Secondary inoculations resulted in an IgM and IgG titer augmentation in 1 or 5 larvae-inoculated animals to levels comparable to those of animals inoculated with 20 larvae, but titers in high inoculum animals did not increase upon secondary inoculation. Primary inoculation induced low ES-specific IgE antibody titers. However, secondary inoculation produced a different pattern than with IgM or IgG titers. Instead of titers equivalent to animals receiving more larvae, rats receiving 1 larva developed higher IgE titers than rats receiving larger inoculums. IgE titers of single larvae-inoculated rats peaked at 3-5 days after secondary inoculation but disappeared by day 14. The time course of IgE production is therefore consistent with duration of the infection. As the natural infection typically involves few larvae, monitoring ES-specific IgE may be a useful diagnostic tool for human intestinal anisakiasis.

Ferredoxin-dependent redox system of a thermoacidophilic archaeon, Sulfolobus sp. strain 7. Purification and characterization of a novel reduced ferredoxin-reoxidizing iron-sulfur flavoprotein

To elucidate the ferredoxin-dependent redox system of the thermoacidophilic, aerobic archaeon Sulfolobus sp. strain 7, a novel FeS flavoprotein, which can reoxidize the reduced 7Fe ferredoxin in vitro, has been purified and characterized (designated as IFP) using the cognate 7Fe ferredoxin and 2-oxoacid:ferredoxin oxidoreductase, a key enzyme of the archaeal tricarboxylic acid cycle. IFP consists of three non-identical subunits with apparent molecular masses of 87, 32, and 22 kDa, respectively, and contains at least two FMN (Em, 6.8 = -57 mV) and two plant-ferredoxin-type [2Fe-2S]2+,1+ clusters (Em, 6.8 = -260 mV)/alpha 2 beta 2 gamma 2 structure. Both FeS and flavin centers of IFP are slowly but fully reduced by the enzymatically reduced cognate ferredoxin under anaerobic conditions at 50 degrees C, but not by NAD(P)H. Thus, the ferredoxin-dependent redox system of Sulfolobus sp. strain 7 is tentatively proposed as follows: 2-oxoacid:ferredoxin oxidoreductase (thiamine pyrophosphate and [4Fe-4S] cluster)-->ferredoxin-->IFP ([2Fe-2S] cluster-->FMN).

Intravenous administration of L-arginine inhibits angiotensin-converting enzyme in humans

The iv administration of L-arginine, a precursor of endothelium-derived relaxing factor/nitric oxide, is known to decrease blood pressure in humans by its direct vasodilatory effects. The purpose of the present study was to determine whether L-arginine infusion modifies the renin-angiotensin (Ang)-aldosterone system as well as blood pressure and renal hemodynamics. L-Arginine and saline vehicle were iv administered to 10 healthy male subjects in random order on different days. L-Arginine infusion (500 mg/kg over 30 min) decreased mean blood pressure (from 81.2 +/- 2.7 to 74.0 +/- 2.5 mm Hg; P < 0.001) and renal vascular resistance (from 0.085 +/- 0.007 to 0.074 +/- 0.006 mm Hg/mL.min; P < 0.01) and increased heart rate (from 60.3 +/- 2.7 to 69.7 +/- 2.1 beats/min; P < 0.001) and renal plasma flow (from 616.6 +/- 37.8 to 701.0 +/- 49.2 mL/min; P < 0.05). L-Arginine reduced serum Ang-converting enzyme activity (from 10.4 +/- 0.6 to 8.9 +/- 0.5 nmol/mL.min; P < 0.05) and plasma Ang-II (from 19.3 +/- 3.3 to 12.7 +/- 2.8 pg/mL; P < 0.001), but had no effect on PRA or the glomerular filtration rate. The saline vehicle did not alter any of these parameters. The iv administration of L-arginine (endothelium-derived relaxing factor/nitric oxide) may reduce the plasma Ang-II concentration by inhibiting Ang-converting enzyme. The mechanism by which L-arginine infusion decreases blood pressure can be at least in part explained by inhibition of the renin-Ang system.

Regulation of lrp gene expression by H-NS and Lrp proteins in Escherichia coli: dominant negative mutations in lrp

Lrp (leucine-responsive regulatory protein) is a global transcription factor of Escherichia coli and regulates, negatively or positively, many genes including lysU, which encodes lysyl-tRNA synthetase. Dominant negative mutations that derepress lysU expression were isolated in this study. These mutations affected a predicted DNA-binding domain of Lrp and mutants were defective DNA-binding domain of Lrp and mutants were defective both in activation of ilvIH expression and in repression of lysU expression. Consistent with the previous notion that lrp is autoregulated, lrp expression was derepressed by these mutations and repressed by multi-copy plasmids carrying lrp+. Moreover, we found by gene fusion and Northern blot hybridization that the "histone-like" protein, H-NS, bound specifically to a promoter segment of lrp in vitro, and the level of lrp expression increased in the hns null mutant. These results indicated that the lrp gene is not only feedback regulated by Lrp but is also controlled by H-NS protein.

Screening of stable proteins in an extreme thermophile, Thermus thermophilus

The leuB gene codes for 3-isopropylmalate dehydrogenase of the leucine biosynthetic pathway in an extreme thermophile, Thermus thermophilus. The leuB gene of the thermophile was replaced with a temperature-sensitive chimeric leuB gene. The resultant transformant was adapted to high temperature, a thermostable mutant strain being obtained. A single base substitution that replaces isoleucine at 93 with leucine was found in the chimeric leuB gene of the thermostable mutant. The resultant amino acid residue coincided with the corresponding residue of the T. thermophilus enzyme. It was confirmed that the mutant enzyme is more stable than the original chimeric enzyme. This system can be used to produce stabilized mutants of other enzymes without structural knowledge of them.

Assessment of platelet cytosolic concentration of free magnesium in healthy subjects

We measured basal cytosolic concentration of free Mg2+ ([Mg2+]i) in platelets from 30 healthy volunteers by using mag-fura-2, a new fluorescent Mg2+ indicator. The mean [Mg2+]i was 381 +/- 22 mumol/L, with values ranging from 226 to 771 mumol/L. The day-to-day intrasubject coefficient of variation was relatively small (3.6%). [Mg2+]i was significantly higher in men than in women (430 +/- 38 vs 332 +/- 17 mumol/L, p < 0.03), and was not correlated with age. There was no significant relation between platelet [Mg2+]i and serum total Mg concentration. The results indicate that the gender but not age may decide intracellular Mg2+ status. In addition, the mechanisms that regulate [Mg2+]i may be independent of those that influence the extracellular concentration of Mg.

His273 of 3-isopropylmalate dehydrogenase from Thermus thermophilus HB8 is involved in the coenzyme binding

The coenzyme binding site of NAD(+)-dependent 3-isopropylmalate dehydrogenase from Thermus thermophilus was analyzed by chemical modification and site-directed mutagenesis, and His273 of the enzyme was identified to be involved in the coenzyme binding.

Sulredoxin: a novel iron-sulfur protein of the thermoacidophilic archaeon Sulfolobus sp. strain 7 with a Rieske-type [2Fe-2S] center

A novel pink [2Fe-2S] protein has been purified from the cytosol fraction of the thermoacidophilic archaeon Sulfolobus sp. strain 7 (originally named Sulfolobus acidocaldarius 7) and called "sulredoxin." Its absorption, circular dichroism, and electron paramagnetic resonance spectra suggest the presence of a Rieske-type [2Fe-2S] cluster (g-factors of 2.01, 1.91, and 1.79; average g-factor [gav] = 1.90) which is remarkably similar to that of Thermus thermophilus respiratory Rieske FeS protein (J. A. Fee, K. L. Findling, T. Yoshida, R. Hille, G. E. Tarr, D. O. Hearshen, W. R. Dunham, E. P. Day, T. A. Kent, and E. Münck, J. Biol. Chem. 259:124-133, 1984) and distinctively different from those of the plant-type ferredoxins (gav = 1.96). Sulredoxin, which is the first Rieske-type [2Fe-2S] protein isolated from an archaeal species, does not function as an electron acceptor of the cognate 2-oxoacid:ferredoxin oxidoreductase. Whether sulredoxin is derived from the archaeal membrane-bound respiratory Rieske-type FeS center (gy = 1.91) is the subject of further investigation.

Effects of L-arginine infusion on renal hemodynamics in patients with mild essential hypertension

Previous studies have shown that endothelium-derived relaxing factor/nitric oxide plays an important role in the regulation of systemic and renal hemodynamics. The purpose of the present study was to determine whether endothelium-dependent renovascular relaxation was impaired in patients with mild essential hypertension who had normal renal plasma flow and glomerular filtration rate. We evaluated the effects of intravenous administration of L-arginine on blood pressure and renal hemodynamics in 13 patients with mild essential hypertension and 15 normotensive control subjects. L-Arginine infusion (500 mg/kg over 30 minutes) reduced mean blood pressure (from 82.5 +/- 2.5 to 76.3 +/- 2.6 mm Hg in hypertensive patients and from 106.1 +/- 3.0 to 97.5 +/- 2.9 mm Hg in control subjects; P < .001) and renovascular resistance (from 0.084 +/- 0.009 to 0.067 +/- 0.009 mm Hg.mL-1.min-1.[1.48 m2]-1 and from 0.105 +/- 0.010 to 0.093 +/- 0.011 mm Hg.mL-1.min-1.[1.48 m2]-1, respectively; P < .001). L-Arginine infusion increased renal plasma flow (from 602 +/- 36 to 698 +/- 40 mL.min-1.[1.48 m2]-1, P < .05) in normotensive subjects but not in hypertensive subjects, and glomerular filtration rate was unaffected in both groups. Although the L-arginine-induced reduction in mean blood pressure was similar in both groups, the decline in renovascular resistance was smaller in hypertensive subjects. The response of renal plasma flow was also smaller in hypertensive subjects. These findings suggest that dysfunction of the L-arginine-nitric oxide pathway exists in the renal circulation even in mild essential hypertension with normal renal plasma flow and glomerular filtration rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Systemic magnesium deficiency disclosed by magnesium loading test in patients with essential hypertension

The present study was designed to determine whether magnesium (Mg) deficiency is present in patients with essential hypertension. We measured the retention of an intravenously administered Mg load (0.2 mmol/kg MgSO4 over 4 h), and serum and erythrocyte Mg concentrations in 17 inpatients with essential hypertension and in 15 normotensive controls. There was no significant difference between the two groups in erythrocyte Mg concentration (normotensives vs., hypertensives: 2.0 +/- 0.5 vs. 2.1 +/- 0.4 mmol/l cells), serum Mg concentration (normotensives vs. hypertensive: 2.1 +/- 0.2 vs. 2.1 +/- 0.2 mg/dl), or in urinary Mg excretion (normotensives vs. hypertensives: 65.8 +/- 25.5 vs. 73.7 +/- 26.7 mg/day). However, Mg retention was significantly higher in hypertensives than in normotensives (normotensives vs. hypertensives: 31.8 +/- 12.1 vs. 41.9 +/- 13.3%). These results suggest that a systemic Mg deficiency, which is undectectable by serum or erythrocyte Mg determination, may exist in patients with essential hypertension.