Reversal of HO-1 related cytoprotection with increased expression is due to reactive iron

It is often postulated that the cytoprotective nature of heme oxygenase (HO-1) explains the inducible nature of this enzyme. However, the mechanisms by which protection occurs are not verified by systematic evaluation of the physiological effects of HO. To explain how induction of HO-1 results in protection against oxygen toxicity, hamster fibroblasts (HA-1) were stably transfected with a tetracycline response plasmid containing the full-length rat HO-1 cDNA construct to allow for regulation of gene expression by varying concentrations of doxycycline (Dox). Transfected cells were exposed to hyperoxia (95% O(2)/5% CO2) for 24 h and several markers of oxidative injury were measured. With varying concentrations of Dox, HO activity was regulated between 3- and 17-fold. Despite cytoprotection with low (less than fivefold) HO activity, high levels of HO-1 expression (greater than 15-fold) were associated with significant oxygen cytotoxicity. Levels of non-heme reactive iron correlated with cellular injury in hyperoxia whereas lower levels of heme were associated with cytoprotection. Cellular levels of cyclic GMP and bilirubin were not significantly altered by modification of HO activity, precluding a substantial role for activation of guanylate cyclase by carbon monoxide or for accumulation of bile pigments in the physiological consequences of HO-1 overexpression. Inhibition of HO activity or chelation of cellular iron prior to hyperoxic exposure decreased reactive iron levels in the samples and significantly reduced oxygen toxicity. We conclude that there is a beneficial threshold of HO-1 overexpression related to the accumulation of reactive iron released in the degradation of heme. Therefore, despite the ready induction of HO-1 in oxidant stress, accumulation of reactive iron formed makes it unlikely that exaggerated expression of HO-1 is a cytoprotective response.

[Determination of inosine 5'-monophosphate and guanosine 5'-monophosphate in taste-enhancers by ion chromatography]

A high performance anion-exchange chromatographic method was developed for the simultaneous determination of two kinds of taste-enhancers, inosine 5'-monophosphate (IMP) and guanosine 5'-monophosphate (GMP), in the presence of monosodium glutamate and chloride (salt). The separation was achieved by using Dionex IonPac AG11 and IonPac AS11 columns, and the determination by ultraviolet absorbance detection at 254 nm. The detection limits (S/N = 3) were 0.21 mg/L and 0.27 mg/L for IMP and GMP, respectively. Good linearities between the concentrations of the two analytes and relevant peak area responses were obtained in the range of 2-100 mg/L. Under the experimental conditions, glutamate, chloride, succinate, benzoate, sorbic acid and citrate did not interfere in the determination of IMP and GMP. The method has been successfully applied to the determination of IMP and GMP in gourmet powder as well as chicken bouillon, and the average recoveries for various samples ranged from 97% to 103%.

Natriuretic peptides in the lung modulated by pneumonectomy

BACKGROUND

Natriuretic peptides are vasodilator hormones involved in the regulation of blood pressure and volume homeostasis. However, the mechanism of these peptides after pneumonectomy remains obscure.

METHODS

We investigated changes in the pulmonary arterial pressure and the localization and changes in the atrial (A-type) natriuretic peptide (ANP) and the C-type natriuretic peptide (CNP) in the lung, using immunohistochemistry and radioimmunoassay (RIA) in anesthetized dogs. Furthermore, we examined guanosine 3', 5'-monophosphate (cGMP) levels in plasma and in the contralateral lung.

RESULTS

Pulmonary arterial pressure was significantly increased after pneumonectomy. The immunoreactivities of both ANP and CNP were detected in the endothelium of the pulmonary artery. In the contralateral lung, the concentrations of ANP and CNP were both significantly increased. In plasma, only ANP levels were significantly increased. In contrast, the plasma and lung cGMP levels were significantly reduced after pneumonectomy.

CONCLUSIONS

We postulate that the processes from secretion in the vascular endothelial cells to the action via ANP and CNP receptors are effected in the contralateral lung tissue at the acute stage of pneumonectomy.

An improved 32P-postlabeling/high-performance liquid chromatography method for the analysis of the malondialdehye-derived 1, N2-propanodeoxyguanosine DNA adduct in animal and human tissues

Malondialdehyde (MDA) is a major lipid peroxidation product that is mutagenic and tumorigenic. The MDA-modified DNA adduct, 3-(2-deoxy-beta-D-erythro-pentofuranosyl)pyrimido[1, 2-alpha]purin-10(3H)-one (M1G), has been detected in human tissues and may be a marker of human cancer risk. In this paper, we describe an improved 32P-postlabeling/HPLC method for sensitive detection and quantitation of this MDA-modified 2'-deoxyribonucleotide adduct. Specific improvements include (i) unequivocal structural identification of the postlabeling products, both the 3', 5'-bisphosphate of M1G (MDA-3',5'-dGDP) and the 5'-monophosphate of M1G (MDA-5'-dGMP); (ii) efficient separation of the 32P-postlabeling products by HPLC; and (iii) the incorporation of a synthetically prepared MDA-modified DNA (or the 3'-monophosphate of M1G) with a known modification level as an internal standard. This improved quantitative methodology provides high intra- and inter-assay reproducibility and has been applied to the analysis of this adduct in rodent and human samples.

Effects of cardiopulmonary bypass and inhaled nitric oxide on platelets in children with congenital heart defects

Nitric oxide (NO) reduces platelet aggregation in vitro. However, repeated measurements of platelet aggregation in infants and small children are impossible due to the large blood samples required. Instead, the expression of different platelet receptors mediating platelet adhesion (CD 36 and CD 42b), activation (CD 42b and CD 61) and aggregation (CD 41a) was measured repeatedly by flow cytometry. First, the expression of platelet receptors was quantified in platelet suspensions of 20 healthy volunteers after incubation with different concentrations of NO (0, 25, 100 and 640 ppm) and compared to changes in platelet aggregation and intrathrombocytic cGMP levels. It was then studied in 21 infants and children before, during and up to 3 days after cardiopulmonary bypass surgery. Seven of these patients required NO inhalation postoperatively. The in vitro experiments showed a reduced expression of the CD 41a, CD 42b and CD 61 receptors with increasing doses of NO, predominantly affecting the CD 41a receptor (-11% at 100 ppm and -20% at 640 ppm). This significant effect is in keeping with the observed NO-induced inhibition of platelet aggregation (-44% at 100 ppm) and the rise in platelet cGMP levels (+69% at 100 ppm). In patients without inhaled NO, the expression of CD 41a was slightly attenuated during cardiopulmonary bypass surgery (-15%) but increased significantly afterwards (2 h: +31%, 1st day: +129%, 2nd day: +120%, 3rd day: +111%). Comparable results were obtained regarding the other adhesion molecules CD 36, CD 42b and CD 61. In patients with inhaled NO the same pattern was observed and analysis of variance did not reveal any significant difference between both groups of patients.

CONCLUSIONS

NO (> or = 100 ppm) decreases the expression of different platelet adhesion molecules and platelet aggregation, presumably via an increase in intracellular cGMP. However, due to the low dose range used in the clinical setting (1-40 ppm) this is clinically not relevant. Immediately after cardiopulmonary bypass surgery the expression of these adhesion molecules is reduced, but recovers on the 1st postoperative day.

32P-postlabelling approaches for the detection of 8-oxo-2'-deoxyguanosine-3'-monophosphate in DNA

32P-Postlabelling methods have been investigated for the analysis of the oxidative DNA damage lesion 8-oxoguanine. The extent of digestion of commercially available calf thymus DNA and an 8-oxo-2'-deoxyguanosine-3'-monophosphate (8oxodGp) containing oligonucleotide to 2'-deoxynucleotide-3'-monophosphates, using calf spleen phosphodiesterase and micrococcal nuclease, was determined by HPLC. The extent of unmodified nucleotide release from DNA, and the extent of 8oxodGp released from the oligomer did not increase between 1 and 16 h of incubation at 37 degrees C. Normal nucleotide release from DNA was found to be quantitative under these conditions, and 8oxodGp release from the oligomer was in the range of 84-91%. RNA contamination in DNA prepared for 32P-postlabelling severely compromised 8oxodGp analysis. Guanosine-3'-monophosphate (Gp) was found to exhibit similar chromatographic and electrophoretic properties to 8oxodGp and as such compromised both 8oxodGp isolation in enrichment steps and subsequent resolution of the 32P-labelled bisnucleotides by TLC. The effect of ribonuclease A, T1 and T2 was investigated and a combination of A + T1 was found to reduce Gp contamination in DNA samples to levels which no longer interfered with 8oxodGp analysis. We have successfully applied an HPLC enrichment protocol to the analysis of 8oxodGp in calf thymus DNA. Since determination of damage levels in human samples is often restricted by the amount of DNA available for analysis, a novel capillary electrophoresis (CE) technique for the enrichment of 8oxodGp has been developed. The advantage of CE is that it can achieve resolution of 8oxodGp and unmodified deoxynucleotides from much smaller samples and minimises the amount of [gamma-32P]ATP necessary for the analysis.

Characterisation of the pterin molybdenum cofactor in dimethylsulfoxide reductase of Rhodobacter capsulatus

Analysis of dimethylsulfoxide reductase from Rhodobacter capsulatus showed that it contained 1 mol Mo and 2 mol GMP. This indicates that the molybdenum cofactor in dimethylsulfoxide reductase is bis(molybdopterin guanine dinucleotide) molybdenum. The absorption spectrum of the molybdopterin guanine dinucleotide released from dimethylsulfoxide reductase after denaturation of the holoenzyme was compared with those of pterin standards of known redox state. The spectra were most similar to pterin standards in the dihydro state and oxidised state. The reduction of 2,6-dichloroindophenol by molybdopterin guanine dinucleotide released from dimethylsulfoxide reductase and by pterin standards was also measured and approximately 2 mol electrons/2 mol molybdopterin guanine dinucleotide were found to reduce 2,6-dichloroindophenol. These results are consistent with the presence of one molybdopterin guanine dinucleotide moiety with a pyrazine ring at the oxidation level of a dihydropteridine and one molybdopterin guanine dinucleotide moiety with a pyrazine ring at the oxidation level of a fully aromatic pteridine. It is suggested that the pyrazine ring of Q-molybdopterin guanine dinucleotide is fully aromatic and contains a 5,6 double bond.

Mechanisms of changes in renal handling of sodium following transjugular intrahepatic portal systemic stent-shunt (TIPSS)

BACKGROUND AND AIMS

Transjugular intrahepatic portosystemic stent-shunt (TIPSS) reduces the portal pressure gradient and leads to better control of ascites. The aim of this study was to evaluate (1) changes in renal handling of sodium following TIPSS and (2) the mechanism of these changes.

DESIGN

Prospective study.

SETTING

Tertiary referral centre for liver diseases.

METHODS

Eighteen patients with ascites undergoing TIPSS for recurrent variceal haemorrhage (16) (3 or more hospital admissions because of variceal haemorrhage whilst being treated endoscopically) or refractory ascites (2) were studied. Urinary sodium (UNa), creatinine clearance (CrCl), plasma renin activity (PRA), atrial natriuretic peptide (ANP), cyclic guanosine monophosphate (cGMP), Angiotensin II (AII) and lithium clearance (LiCl) were measured before and 3 months after TIPSS when portography was performed and the portal pressure gradient (PPG) also measured. All patients were haemodynamically stable and had received no diuretics for at least 1 week before blood sampling.

RESULTS

Improvement in ascites was achieved in all patients in whom TIPSS was inserted successfully (reduction in PPG to < 12 mmHg). PPG was reduced from a mean of 19 (+/-6) to 8.8 (+/-3.4) mmHg (P < 0.001). Urinary sodium and creatinine clearance improved significantly following TIPSS (P < 0.001, P < 0.001, respectively). PRA, All, cGMP and LiCl were abnormal before TIPSS and improved significantly following TIPSS (P < 0.007, P < 0.001, P < 0.001 and P < 0.01, respectively). ANP was not significantly different from normal controls and did not change significantly following TIPSS. Changes in UNa did not correlate with the Pugh score or the change in PPG.

CONCLUSION

The results of this study show that TIPSS is associated with significant improvement in UNa, CrCl, PRA, AII, cGMP and LiCl. The change in UNa following TIPSS was independent of the severity of underlying liver disease or the change in PPG.

Development of a 32P-postlabelling method for the analysis of adducts arising through the reaction of acetaldehyde with 2'-deoxyguanosine-3'-monophosphate and DNA

A 32P-postlabelling assay was developed for the analysis of adducts arising from the reaction of 2'-deoxyguanosine-3'-monophosphate with acetaldehyde, the primary oxidative metabolite of ethanol. The 32P-postlabelling reaction was optimized by testing various parameters such as the kinetics of phosphorylation by T4 polynucleotide kinase, substrate-concentration-dependent labelling efficiency and the concentration of the various ingredients of the phosphorylation reaction. The sensitivity to 3'-monophosphate dephosphorylation activity of nuclease P1 was also studied. Three stable adducts were separated by reversed-phase HPLC. The major stable adduct was structurally characterized and identified as N2-ethyl-2'-deoxyguanosine and could be detected, after reduction with NaBH4 or a mixture of ascorbic acid and GSH, in calf thymus DNA samples that had been reacted in vitro with acetaldehyde. DNA adducts were isolated after enzymatic digestion to mononucleotides followed by nuclease P1 digestion of normal nucleotides. The average levels of acetaldehyde-DNA adducts detected in these samples were 12.1 +/- 2.3 (n = 17) and 4.9 +/- 0.9 (n = 9) adducts/10(7) nucleotides after reduction with NaBH4, or ascorbic acid and GSH respectively. The 32P-postlabelling method was further validated by the detection of acetaldehyde adducts in liver DNA from mice treated with ethanol. The average concentration of the adducts detected in these animals was 1.5 +/- 0.8 (n = 7) adducts/10(8) nucleotides, as analyzed by reversed-phase HPLC with online detection of radioactivity.

Bioluminescent determination of 0.1 picomole amounts of guanine nucleotides

A bioluminescence procedure for the determination of the guanylates has been optimized to allow measurement of 0.1 pmol amounts. Modifications of the Karl procedure include the use of purified firefly luciferase and nucleoside diphosphate kinase instead of a crude extract of firefly tails, the use of Tricine buffer instead of the inhibitory arsenate buffer, and optimization of the amounts of reagents and incubation times for each of the partial reactions. In the determination of GMP, background values varied widely with different lots of bovine guanylate kinase. Careful selection of a suitable lot of bovine brain guanylate kinase was essential for determination of lower amounts of guanylates. This establishes that selection of guanylate kinase must be based on experimental determination and not reported adenylate kinase activity. The wide variation in background was not eliminated by the inclusion of adenylate kinase inhibitors.

Simultaneous determination of flavor enhancers inosine 5'-monophosphate and guanosine 5'-monophosphate in food preparations by derivative spectrophotometry

A derivative spectrophotometric method was developed for the quantitative determination of 2 flavor enhancers, inosine 5'-monophosphate (IMP) and guanosine 5'-monophosphate (GMP), in the presence of monosodium glutamate (MSG). Procedures for determining IMP and GMP singly and in binary mixtures are described. Overlapping absorption spectra of both compounds were resolved by using first-derivative spectrophotometry. By measuring the first-derivative signals of IMP and GMP at 253 and 248 nm, respectively, simultaneous determination was possible for IMP and GMP at 5-40 micrograms/mL, in the presence of up to 5000 micrograms/mL MSG. The method was satisfactorily used to determine IMP and GMP in several food preparations.

7-Alkyldeoxyguanosine adduct detection by two-step HPLC and the 32P-postlabeling assay

7-Alkyldeoxyguanosine DNA adducts may be a marker for some N-nitroso compound exposures and subsequent human cancer risk. A sensitive and highly specific assay for the detection of 7-methyl-2'-deoxyguanosine-3'-monophosphate (7-methyldGp) and 7-ethyl-2'-deoxyguanosine-3'-monophosphate (7-ethyldGp) has been developed by combining two different HPLC purification steps with the 32P-postlabeling assay. We previously reported that ion-pair reverse-phase (IP) chromatography coupled with the 32P-postlabeling assay detects 7-methyldGp in human lung, but have found that other nucleotides and unknown adducts co-elute. Thus, weak anion exchange (AE) HPLC was added in tandem with IP HPLC prior to the 32P-postlabeling assay. 2'-Deoxyguanosine-3'-monophosphate (dGp) is incorporated into the assay as an internal standard for the assessment of enzyme labeling efficiency and adduct recovery. The methodology was validated using radiolabeled DNA and liquid scintillation counting, which accounts for adduct loss from enzymatic digestion to detection. Levels of 7-ethyldGp also were correlated with accelerator mass spectrometry. The overall adduct recovery with this method was 58% for 7-methyldGp and 98% for 7-ethyldGp. The detection limit for both assays using 100 micrograms of DNA was one adduct in 10(8) unmodified dGp. 7-MethyldGp and 7-ethyldGp levels were determined in ten human lung samples at levels of 1.4-5.4 and 0.6-3.1 adducts per 10(7) dGp respectively, and in five human lymphocyte samples at levels of 5.0-8.3 and 0.3-1.4 adducts per 10(7) dGp respectively. Combining the two HPLC purification steps and the 32P-postlabeling assay attains chemical specificity, retains sufficient quantitative sensitivity and should be useful in human biomonitoring studies.

The distribution and colocalization of neuropeptides in perivascular nerves innervating the large arteries and veins of the snake, Elaphe obsoleta

Single- and dual-labelling immunohistochemistry were used to determine the distribution and coexistence of neuropeptides in perivascular nerves of the large arteries and veins of the snake, Elaphe obsoleta, using antibodies for vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide, neuropeptide Y, galanin, somatostatin, and leu-enkephalin. Blood vessels were sampled from four regions along the body of the snake: region 1, arteries and veins anterior to the heart; region 2, central vasculature 5 cm anterior and 10 cm posterior to the heart; region 3, arteries and veins in a 30-cm region posterior to the liver; and region 4, dorsal aorta and renal arteries, renal and intestinal veins, 5-30 cm cephalad of the vent. A moderate to dense distribution of vasoactive intestinal polypeptide-like immunoreactive fibres was found in most arteries and veins of regions 1-3, but fibres were absent from the vessels of region 4. The majority of vasoactive intestinal polypeptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were unaffected by either capsaicin or 6-hydroxydopamine (6-OHDA) pretreatment. In the anterior section of the snake, the vagal trunks contained many cell bodies with colocalized vasoactive intestinal polypeptide and substance P-like immunoreactivity. It is suggested that the vasoactive intestinal polypeptide/substance P-like immunoreactive cell bodies and fibres are parasympathetic postganglionic nerves. Neuropeptide Y-like immunoreactive fibres were observed in all arteries and veins, being most dense in regions 3 and 4. The majority of these fibres also contained colocalized galanin-like immunoreactivity, and were absent in tissues from 6-OHDA pretreated snakes, suggesting that neuropeptide Y and galanin are colocalized in adrenergic nerves. A small number of neuropeptide Y-like immunoreactive fibres contained vasoactive intestinal polypeptide but not galanin, and were unaffected by 6-OHDA treatment. All calcitonin gene-related peptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were observed in all vessels, being particularly dense in the carotid artery and jugular veins. All calcitonin gene-related peptide/substance P-like immunoreactive fibres appeared damaged after capsaicin treatment suggesting they represent fibres from afferent sensory neurons. A sparse plexus of somatostatin-like immunoreactive fibres was observed in the vessels only from region 4. No enkephalin-like immunoreactive fibres were found in any blood vessels from any region. This study provides morphological evidence to suggest that there is considerable functional specialization within the components of the rat snake peripheral autonomic system controlling the circulation, in particular the regulation of venous capacitance.

Regulation of platelet clearance receptors for atrial natriuretic peptide in diabetic nephropathy

The findings that circulating levels of atrial natriuretic peptide (ANP) are elevated in diabetic nephropathy and that the magnitude of the urinary excretion rate of cGMP in response to hypervolemia-induced ANP release is blunted have recently been reported. The purpose of this study was to determine whether these abnormalities are associated with the down-regulation of ANP receptors. Because biologically active (A) ANP receptors in the kidney are inaccessible, we have examined the binding of (125I alpha)ANP to clearance (C) receptors on platelets obtained from patients with diabetic nephropathy. Scatchard analysis revealed a reduction in such binding sites compared with those in healthy controls: 12 +/- 2 versus 19 +/- 2 per platelet, respectively (P less than 0.001). The dissociation constant, Kd, was higher: 66.7 +/- 33.1 versus 38.5 +/- 11 pM, respectively (P less than 0.02). The reduced number of receptors could reflect the down-regulation of ANP C receptors in response to an elevation of plasma levels of ANP, the median value of which was 10.6 versus 7.1 pmol/L in controls (P less than 0.05). Alternatively, the findings could represent a primary adaptation by C receptors to elevate plasma ANP levels and increase the availability of the peptide to biologically active renal receptors. The latter adaptation would serve to mitigate the sodium retention that attends diabetic nephropathy.

Alterations in nucleoside monophosphate concentrations in 3LL tumours after combined treatment with tiazofurin and 5-hexyl-2'-deoxyuridine

The IMP and GMP concentrations were compared after treatment with tiazofurin alone and in combination with 5-hexyl-2'-deoxyuridine (HUdR) in 3LL-HH adenocarcinoma in vivo. The elevation in IMP/GMP ratio, indicating guanylate depletion and increase of inosine-5'-monophosphate concentration, showed a dose dependence and was the highest at the 7th hour after treatment with tiazofurin. HUdR application alone caused only a modest change in the nucleotide concentration of LL-HH tumour. However, the rise of IMP but not the reduction of guanylate concentration induced by tiazofurin was remarkably mitigated by HUdR treatment, without affecting the antitumour potency of tiazofurin. Thus HUdR showed modifying activity on some of the tiazofurin-induced changes in nucleotide metabolism which appeared not to be associated with the antiproliferative activity of tiazofurin. It follows that reduced GMP concentration and not the elevation of IMP/GMP ratio could predict therapeutic responses to tiazofurin.

Molybdenum cofactor biosynthesis in Escherichia coli. Requirement of the chlB gene product for the formation of molybdopterin guanine dinucleotide

The chlorate-resistant mutants of Escherichia coli are affected in the biosynthesis of the molybdenum cofactor and show pleiotropic loss of the activities of those enzymes which require the cofactor. The molybdenum cofactor in all molybdoenzymes other than nitrogenase is a complex of the metal with a unique pterin termed molybdopterin. The molybdenum cofactor in a number of E. coli enzymes has been shown to contain GMP in addition to the metal-molybdopterin complex, with the GMP appended in pyrophosphate linkage to the terminal phosphate ester on the molybdopterin side chain. In this paper, we have examined the biochemistry of the chlB mutant and show that the gene product of the chlB locus is essential for the addition of the GMP moiety to form molybdopterin guanine dinucleotide, a step which occurs late in the cofactor biosynthetic pathway in E. coli. Sensitive techniques were developed for the identification of fluorescent derivatives of molybdopterin and of molybdopterin guanine dinucleotide in extracts of E. coli cells. Wild type cells were shown to contain both molybdopterin and molybdopterin guanine dinucleotide, while cells of chlB mutants were found to contain elevated levels of molybdopterin but no detectable molybdopterin guanine dinucleotide.

Detection and quantitation of 8-hydroxydeoxyguanosine 5'-monophosphate in X-irradiated calf-thymus DNA by fluorescence postlabeling

8-Hydroxydeoxyguanosine 5'-monophosphate (8-OH dGmp) was synthesized from deoxyguanosine 5'-monophosphate (dGmp) by ascorbic acid in the presence of hydrogen peroxide and labeled with dansyl chloride through a phosphoramidate linkage with ethylenediamine (EDA). A DNA model 8-OHd(TACG), isolated intact by high pressure liquid chromatography (HPLC) from x-irradiated d(TACG) and characterized by nmr, was digested enzymatically to 5'-mononucleotides. The modified nucleotide was enriched by HPLC and dansylated. Analysis of the dansylated product by HPLC, using a fluorescent detector, detected a peak with retention time corresponding to that of the dansyl labeled authentic marker. The same overall procedure was used to detect 8-OHdGmp from x-irradiated calf-thymus DNA. The content of 8-OHdGmp in the irradiated DNA increased linearly with increasing levels of x-irradiation in the dose range of 6-60 Gy.

Radiation inactivation target-size analysis of soluble guanylate cyclase

The soluble form of guanylate cyclase, which is a heterodimer of two subunits with molecular weights of 82,000 and 70,000, was analyzed by radiation inactivation experiments to determine its functional size. Lyophilized crude extract from rat lung or the purified enzyme were irradiated with different doses from 60Co gamma-rays, and the residual activities were measured in the presence or absence of a potent activator, sodium nitroprusside. The target sizes for the basal activity and for the activity in the presence of sodium nitroprusside were calculated from the decay curve was 77 and 192 kDa, respectively, on the crude enzyme, or as 71 and 163 kDa, respectively, on the purified enzyme. The size for the activatable form of the enzyme was more than twice that of the basal activity and close to the size of the holoenzyme, implying that the enzyme activity must reside on one of the subunits and the activation by sodium nitroprusside requires interaction of both subunits.

The preparation and spectroscopic characterization of a weakly self-associating salt of guanylyl-(3'-5')-guanosine

The tetramethylammonium salt of guanylyl-(3'-5')-guanosine has been prepared by a cation-exchange technique and it has been found that the tetramethylammonium ion drastically reduces the self-association of GpG in solution. This has allowed the characterization of GpG by FTIR and 1-D and 2-D NMR spectroscopy. A complete, well-resolved 1H NMR spectrum in D2O has been obtained and all resonances have been assigned. A weak, essentially non-cooperative intermolecular association is observed in solution (15-20 mM) below 40 degrees C. The association occurs via base stacking and base-base hydrogen bonding.

Refined X-ray structure of the low pH form of ribonuclease T1-2'-guanylic acid complex at 1.9 A resolution

The three-dimensional X-ray structure of the RNase T1[EC 3.1.27.3]-2'GMP complex crystallized at low pH value (4.0) was determined, and refined to 1.9 A resolution to give a final R value of 0.203. The refined model includes 781 protein atoms, 24 inhibitor atoms, and 43 solvent molecules. The imidazole rings of His27 and His40 interact with the carboxyl side chains of Glu82 and Glu58, respectively, whereas that of His92 is in contact with the main chain carbonyl oxygen of Ala75. In the complex, the ribose ring of the 2'GMP molecule adopts a C2'-endo puckering, and the exocyclic conformation is gauche(-)-gauche(+). The glycosyl torsion angle is in the syn range with an intramolecular hydrogen bond between N3 and O5', and the 2'-phosphate orientation is trans-gauche(-). The guanine base of the inhibitor is tightly bound to the base recognition site with five hydrogen bonds (N1--Glu46O epsilon 2, N2---Asn98O,O6---Asn44N, and N7 ---Asn43N delta 2/Asn43N) and is sandwiched between the phenolic ring portions of Tyr42 and Tyr45 by stacking interactions. The 2'-phosphate group interacts with Arg77N eta 2, Glu58O episilon 2, and Tyr 38O eta but not with any of the histidine residues. Arg77N eta 2 also interacts with Tyr38O eta. There is no interaction between the ribose moiety of the inhibitor and the enzyme.