Biomedical subjects

C R Jones

Publications and source records attributed to C R Jones.

At least 19 recordsLinked to original sources

PubMed1992

Induction of a pleiotropic response by phenobarbital and related compounds. Response in various inbred strains of rats, response in various species and the induction of aldehyde dehydrogenase in Copenhagen rats.

The ability of phenobarbital (PB) to induce a "pleiotropic response" which includes both cytochromes P450 (CYP) as well as other drug-metabolizing enzymes was investigated in mice, rabbits, hamsters, and various inbred strains of rats. PB induced similar drug-metabolizing enzymes (CYP2B, CYP3A, and epoxide hydrolase) in rats, mice, rabbits and hamsters. PB and two structural analogues (ethylphenylhydantoin and barbital) induced a variety of drug-metabolizing enzymes (CYP2B, CYP3A, CYP2A, epoxide hydrolase) in a series of inbred strains of rats. In contrast, levels of aldehyde dehydrogenase (ALDH) (propionaldehyde, NAD+) which were expressed constitutively in all strains of rats were induced by PB in only two of the eight strains (ACI, Copenhagen). Further investigations of ALDH induction by structurally diverse compounds in Copenhagen rats demonstrated a strong correlation between the induction of ALDH and other elements of the pleiotropic response (CYP2B, CYP3A, epoxide hydrolase). These results imply that induction of ALDH (propionaldehyde, NAD+) is associated with the PB pleiotropic response in Copenhagen rats.

Aldehyde Dehydrogenase↗

PubMed1992

A pleiotropic response to phenobarbital-type enzyme inducers in the F344/NCr rat. Effects of chemicals of varied structure.

The effects of a number of phenobarbital-type inducers on selected drug-metabolizing enzymes in male F344/NCr rats were determined by measuring specific catalytic activities and/or by measuring the levels of RNA which hybridize with specific probes for the corresponding genes. The effects on hepatic CYP2B1 were assessed by measuring the levels of CYP2B1-specific RNA and benzyloxyresorufin O-dealkylase and testosterone 16 beta-hydroxylase activities. Levels of CYP3A were monitored by measuring the rate of hydroxylation of testosterone at the 6 beta-position. Microsomal epoxide hydrolase activity was determined by measurement of cellular RNA specific for this form and by assaying the hydrolysis of benzo[a]pyrene-4,5-oxide. UDP-glucuronyltransferase activity was assayed by measuring the glucuronidation of 3-hydroxybenz[a]anthracene. Levels of glutathione S-transferase Ya/Yc were measured by quantifying total cellular RNA coding for the proteins. When male F344/NCr rats were administered various doses of phenobarbital or dichlorodiphenyltrichloroethane (DDT), strong correlations between the induction of CYP2B1 and the induction of epoxide hydrolase or UDP-glucuronyltransferase activities were observed. Treatment of rats with barbiturates, hydantoins, halogenated pesticides such as DDT or alpha-hexachlorocyclohexane, 2,4,5,2',4',5'-hexachlorobiphenyl, CYP2B1 inhibitors such as clotrimazole or clonazepam, or such structurally-diverse compounds as 2-hexanone or diallyl sulfide resulted in induction of CYP2B1-mediated enzyme activity and induction of certain other forms of cytochrome P450, microsomal epoxide hydrolase, at least one form of UDP-glucuronyltransferase, and multiple forms of glutathione S-transferase. This suggests that, as a class, compounds which induce CYP2B1 also induce a coordinate hepatic pleiotropic response which includes induction of these other phase I and phase II drug-metabolizing enzymes.

Animals↗

PubMed1992

A markedly diminished pleiotropic response to phenobarbital and structurally-related xenobiotics in Zucker rats in comparison with F344/NCr or DA rats.

Phenobarbital (PB) and certain structurally-related compounds induce a variety of hepatic drug-metabolizing enzymes in many strains of rats. Thus, following administration of PB (300, 500 ppm), barbital (BB, 1500 ppm) or 5-ethyl-5-phenylhydantoin (EPH, 500 ppm), CYP2B1-mediated benzyloxyresorufin O-dealkylase activity and epoxide hydrolase activity were profoundly induced in female DA and F344/NCr rats. In contrast, outbred female lean and obese Zucker rats showed markedly reduced CYP2B1 responses (less than 15% and less than 5% of those observed in the female DA or F344/NCr rat) to PB (doses less than or equal to 300 ppm), BB (1500 ppm) or EPH (500 ppm). In parallel studies, profound increases in RNA levels coding for CYP2B1, glutathione S-transferases Ya/Yc (alpha subclass), or epoxide hydrolase were detected in the female F344/NCr rat following treatment with PB (300 ppm), BB (1500 ppm) or EPH (500 ppm). In contrast, lean Zucker rats showed a strong response only to the highest dose of PB (500 ppm), implying that the diminished response in the Zucker rats may occur at some pretranslational level. Similar studies with lower doses of PB, EPH or BB in male lean Zucker rats showed a decreased response, relative to that in male F344/NCr rats. However, this insensitivity was not as profound as that observed in the female Zucker rats. In fact, the response to PB-type inducers in male or female Zucker rats is probably most clearly explained as a shift of the dose-response curve sharply to the right (decreased responsiveness, compared to F344/NCr or DA rats of the same sex). This decreased responsiveness of female lean Zucker rats to induction of CYP2B1, relative to that of F344/NCr rats, was also observed with the structurally-diverse PB-type inducers clonazepam, clotrimazole and 2-hexanone. In contrast, the female Zucker rat (obese or lean) displayed a pronounced response to induction of CYP1A-mediated ethoxyresorufin O-deethylase activity by beta-naphthoflavone, a prototype inducer of CYP1A1 and CYP1A2. The Zucker rat would thus appear to represent a potentially exploitable genetic model for examining the mechanism of enzyme induction by the myriad xenobiotics which induce a PB-type response.

Animals↗

PubMed1992

Brain dopamine D-2 receptor mechanisms in spontaneously hypertensive rats.

Brain dopaminergic function was studied in spontaneously hypertensive rats (SHR) with the selective dopamine D-2 antagonist sulpiride. Sulpiride dose-dependently inhibited locomotor activity of normotensive Wistar-Kyoto rats (WKY). SHR showed an increase in locomotor activity in response to low doses of sulpiride, whereas no effect was observed of higher doses. In a two-bottle salt-preference test, WKY showed increased preference for an 0.9% saline solution after treatment with sulpiride, whereas total fluid intake remained the same. In SHR, sulpiride influenced neither salt-preference nor total fluid intake. SHR and WKY with a unilateral lesion of the median forebrain bundle showed similar turning behaviour in response to treatment with amphetamine. Pretreatment with 100 mg/kg sulpiride virtually abolished amphetamine-induced turning in WKY, but had little effect in SHR. Sulpiride dose-dependently increased serum prolactin concentrations in WKY and SHR. However, the increase was significantly greater in SHR. Dopamine D-2 receptor binding was measured with in vitro autoradiography, using [125I]-sulpiride as the ligand. Binding density was similar in the caudate nucleus and substantia nigra of SHR and WKY brain. Concentrations of the dopamine metabolites DOPAC and HVA, but not of dopamine itself, were significantly increased in frontal cortex, striatum and hypothalamus after treatment with 100 mg/kg sulpiride. There were no significant differences between SHR and WKY in the increase in the DOPAC/DA and HVA/DA ratio. These data show that SHR show differential changes in their response to central dopamine D-2 blockade when compared to WKY. Thus, in some tests (locomotor activity after high doses, salt preference, turning behaviour), SHR respond less to sulpiride.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗

PubMed1992

Induction of hepatic CYP1A in male F344/NCr rats by dietary exposure to Aroclor 1254: examination of immunochemical, RNA, catalytic, and pharmacokinetic endpoints.

Male F344/NCr rats were exposed to low dietary concentrations of Aroclor 1254 (0-33 ppm) for 7 days, following which the induction of selected hepatic drug metabolizing enzymes was monitored. CYP1A1, measured indirectly by assaying the O-dealkylation of ethoxyresorufin in 9000 g supernatants, was increased 1.5-, 3-, 8-, and 37-fold following 7 days of exposure to 1.0, 3.3, 10, and 33 ppm Aroclor, respectively. In contrast, the O-dealkylation of benzyloxyresorufin, an indirect measure of CYP2B1 activity, was increased approximately 4-fold following exposure to 33 ppm dietary Aroclor. Measurement of the non-P450-mediated activities epoxide hydrolase, DT-diaphorase, and aldehyde dehydrogenase (NADP+, benzaldehyde) revealed < 4-fold inductions following feeding of 33 ppm Aroclor. In view of the relatively high sensitivity of the CYP1A-specific catalytic endpoint as a biomarker for Aroclor exposure, alternative endpoints for detecting induction of this subfamily of P450 were also examined. The extent of in vivo CYP1A induction was assessed by measuring serum concentrations of zoxazolamine 150 min following an intraperitoneal dose of 100 mg/kg body wt. Slight decreases in serum zoxazolamine concentration were observed in rats exposed to as little as 1.0 ppm dietary Aroclor 1254, while profound decreases were seen in rats exposed to > or = to 10 ppm Aroclor. Immunodetection of CYP1A1 protein, with a monoclonal antibody directed against this cytochrome, revealed a 2.9-fold increase in rats exposed to as little as 1.0 ppm Aroclor, and approximately 10- and 44-fold increases following exposure to 3.3 and 10 ppm dietary Aroclor, respectively. Increases in total hepatocellular RNA coding for CYP1A1 and CYP1A2, quantified by hybridization to specific oligonucleotide probes, corresponded well to the increases in hepatic O-dealkylase activity for ethoxyresorufin (CYP1A1) and methoxyresorufin (CYP1A2), respectively. Thus, CYP1A induction, directly or indirectly measured with a variety of endpoints, represents a highly sensitive biomarker for exposure to relatively low doses of Aroclor 1254 in the rat.

Administration, Oral↗

PubMed1992

Induction of various cytochromes CYP2B, CYP2C and CYP3A by phenobarbitone in non-human primates.

Male and female patas (Erythrocebus patas) and cynomolgus (Macaca fascicularis) monkeys were treated with phenobarbitone (PB) and examined for the induction of various cytochrome P450 (P450)-mediated drug metabolizing enzymes. Hydroxylation of testosterone at the 6 beta, 2 beta, and 15 beta positions, metabolites normally associated with CYP3A P450s increased 2- to 5-fold in PB-treated animals. Induction of this P450 family was confirmed by the use of polyclonal antisera directed against the human CYP3A enzymes which inhibited both induced and constitutive 6 beta- and 15 beta-hydroxylase activities in both species of monkeys. The enzymatic activities testosterone 16 beta-hydroxylation, pentoxyresorufin O-dealkylation [PROD], and benzyloxyresorufin O-dealkylation [BZROD] typically associated with the rodent CYP2B subfamily in rodents were also examined. Testosterone 16 beta-hydroxylation activity was highly induced up to 15-fold in both species of monkeys to maximal levels similar to those induced in PB-treated male rats. BZROD was similarly induced up to 10-fold in both species of monkeys, but the maximal levels of BZROD achieved were substantially lower than those obtained in PB-treated rats. Finally, PROD yielded an idiosyncratic response showing substantial induction (> 30-fold) in certain patas monkeys (4 out of 8) but minimal (< 5-fold) induction in the other patas monkeys (4 out of 8) or any of the cynomolgus monkeys (0 out of 8). Immunodetection of various cytochromes using polyclonal antisera directed against rat cytochromes confirmed the induction of CYP3A proteins as well as the induction of protein(s) immunologically cross-reactive with rat CYP2B P450s. BZROD, PROD, or testosterone 16 beta-hydroxylase activities, were not inhibited by antibody to CYP3A P450s. However, high concentrations of polyclonal antiserum directed against rat CYP2B inhibited all three activities in PB-induced patas monkeys. In contrast, this antiserum failed to inhibit the hydroxylation of testosterone at the 6 beta or 2 beta positions. Induction of the CYP2C subfamily was observed by immunochemical detection. Interestingly, induction of this subfamily appeared to be more pronounced in cynomolgus than in patas monkeys. Finally, we failed to observe significant sex-dependent differences in P450-mediated enzymatic activities in either control or induced monkeys. These results confirm the induction of a similar spectrum of P450 proteins by PB in non-human primates to that which has previously been observed in rodents.

Animals↗

PubMed1991

Endothelins: functional and autoradiographic studies in guinea pig trachea.

The presence of binding sites for [125I]endothelin-1 and the contractile activities of endothelins (ETs) and sarafotoxin S6b and the endothelin fragment ET(16-21) were investigated in guinea pig trachea. ETs and sarafotoxin S6b (0.1-100 nM) induced potent contractile responses in guinea pig trachea with EC50 values ranging from 1.57 to 12.97 nM. Epithelium removal increased the potencies of ET-1, ET-2 and S6b, but not that of ET-3, and maximal responses to ET-1 and ET-2 were also increased. Effects of epithelium removal were partially mimicked by phosphoramidon (10 microM), an enkephalinase inhibitor, suggesting that enkephalinase (EC.3.4.24.11.) is able to degrade ET-1 and ET-2. ET-3-induced contractions were not affected by phosphoramidon. Autoradiographic studies suggested the presence of at least two specific binding sites for [125]ET-1 in guinea pig airway smooth muscle. The correlation between Kd and EC50 values suggests that the binding sites identified in the airway smooth muscle represent functional receptors for ETs. ET(16-21) and ET(16-21)-NH2 were less potent agonists than the ETs in guinea pig trachea and 10 microM ET(16-21) was unable to inhibit [125I]ET-1 binding in guinea pig airway smooth muscle. Therefore, these results suggest that the C-terminal hexapeptide of ET-1 cannot be used to classify ET receptors in guinea pig trachea.

Animals↗

PubMed1991

Two-dimensional NMR and structure determination of salmon calcitonin in methanol.

The structure of the 32-residue peptide salmon calcitonin (sCT) in 90% MeOH-10% H2O has been investigated by two-dimensional NMR techniques and molecular modeling. Sequential assignments for nearly all of the 32 spin systems have been obtained, and results indicate that the heptaresidue loop formed by the disulfide bond between Cys-1 and Cys-7 is followed by an alpha-helical segment from Val-8 through Tyr-22. A region of conformational heterogeneity is observed for residues 20-25, resulting from the slow isomerism of the cis and trans forms of Pro-23. The C-terminal segment is found to exist in an extended conformation.

Amides↗

PubMed1991

Induction of cytochrome P450 and other drug metabolizing enzymes in rat liver following dietary exposure to Aroclor 1254.

Selected drug metabolizing activities were measured in female F344/NCr rats exposed to graded dietary concentrations of Aroclor 1254 (1 to 1000 ppm) for 7 days or to lower concentrations of Aroclor (1 to 10 ppm) for up to 28 days. Following the 7-day exposure, the hepatic O-dealkylation of ethoxyresorufin (ETR), mediated primarily by cytochrome P450IA, was increased 60-, 10-, and 4-fold by 33, 10, and 3 ppm Aroclor, respectively. In rats exposed to 10 and 3 ppm Aroclor for 28 days, this activity was increased approximately 30- and 10-fold, respectively. Hepatic ETR O-dealkylase activities correlated with Aroclor concentrations in the livers of exposed rats (r = 0.99, p less than 0.01). Although the O-dealkylation of benzyloxyresorufin was highly increased by 7-days dietary exposure to 1000 ppm Aroclor, the levels of Aroclor necessary for detection of induction were substantially higher than those required for detection of ETR O-dealkylase induction. Examination of the non-P450-mediated drug metabolizing activities, epoxide hydrolase and DT-diaphorase, similarly showed limited (approximately 10-fold) increases. In contrast, aldehyde dehydrogenase (benzaldehyde, NADP+) activity was highly increased (greater than 40-fold) at 1000 ppm, however this activity was increased to only a limited extent at lower Aroclor concentrations (e.g. approximately 3-fold at 33 ppm). These results support the potential use of cytochrome P450 activities as potential biomarkers for environmental exposure to PCBs and related compounds.

Aldehyde Dehydrogenase↗

PubMed1991

Autoradiography of adrenoceptors in rat and human brain: alpha-adrenoceptor and idazoxan binding sites.

This chapter reviews the current classification of adrenoceptors, and notes the difficulties of combining the molecular biological and pharmacological classifications of adrenoceptors. Possibilities for mapping the distribution of the proposed subtypes of adrenoceptors using currently available ligands are discussed, and the autoradiographic visualisation of the broad subtypes of alpha 1-, alpha 2-, beta 1-, and beta 2-adrenoceptors in the rat, monkey and human brain described and illustrated. The non-selectivity of ligands currently being used to label alpha-adrenoceptors is shown; we compare the distribution of [3H]idazoxan binding sites with the distribution of alpha 2-adrenoceptors visualised using other ligands. Resolution limitations of current autoradiographic approaches are considered and we shown how in situ hybridisation can complement data from receptor labelling studies used to localise receptors to pre- or postsynaptic sites.

Animals↗

PubMed1991

Proliferation in human bladder carcinoma measured by Ki-67 antibody labelling: its potential clinical importance.

Ki-67 is a monoclonal antibody which recognises a human nuclear antigen expressed in proliferating cells. The antibody was used to assess proliferation in primary human bladder tumours from 64 patients. Ki-67 index (the number of Ki-67 positive tumour cells divided by the total number of tumour cells %) was derived from 59 tumours. A wide range of Ki-67 indices were recorded, range 3.0-65.8%, mean 20.2%. The Ki-67 index correlated with known prognostic factors: T stage (P = 0.002) and histological grade (P less than 0.001), early stage disease and more differentiated tumours having lower Ki-67 indices. Patients with invasive disease (21 patients) had significantly higher Ki-67 indices than those with non-invasive disease (P = 0.01). Patients with metastatic disease at presentation (four cases) all had a Ki-67 index of greater than or equal to 29%. Ki-67 antibody staining is a simple technique for assessing the proliferation fraction than can be performed on a small amount of tissue taken at routine biopsy without prior injection of thymidine analogues.

Aged↗

PubMed1991

Endothelin receptor heterogeneity; structure activity, autoradiographic and functional studies.

Radioligand binding studies were used to define the binding constants for inhibition of [125I]endothelin-1 binding by endothelin-1 (ET-1), endothelin-3 (ET-3) and a synthetic analogue of ET-1, [Ala1,3,11,15]ET-1 in rat aorta and cerebellum. The inhibition curves for the three substances were similar in the cerebellum (Ki, ET-1 = ET-3 = [Ala1,3,11,15]ET-1) but differed in the aorta (Ki, ET-1 much less than [Ala1,3, 11,15]ET-1) with the ET-3 inhibition curves being biphasic, indicating binding to two sites. In functional studies in the aorta, in contrast to findings in the cerebellum, [Ala1,3,11,15]ET-1 was inactive and ET-3 was a partial agonist. These findings support the idea of heterogeneity of endothelin receptors. Autoradiographic studies were performed to identify the cellular localisation of endothelin-1 receptors in the two tissues. In the aorta binding was to all elements of the vasculature including the endothelium, smooth muscle, periadventitial connective tissue and nerves. In the cerebellum binding sites were located predominantly over the neuronal elements of the granular cell layer. The cellular localisation of the high and low affinity sites for ET-3, and the functional significance of the high affinity binding site for ET-3, remain to be determined.

Animals↗

PubMed1990

Effect of distortions in the deoxyribose phosphate backbone conformation of duplex oligodeoxyribonucleotide dodecamers containing GT, GG, GA, AC, and GU base-pair mismatches on 31P NMR spectra.

We have previously suggested that variations in the 31P chemical shifts of individual phosphates in duplex oligonucleotides are attributable to torsional angle changes in the deoxyribose phosphate backbone. This hypothesis is not directly supported by analysis of the 1H/31P two-dimensional J-resolved spectra of a number of mismatch dodecamer oligonucleotide duplexes including the following sequences: d-(CGTGAATTCGCG), d(CGUGAATTCGCG), d(CGGGAATTCGCG), d(CGAGAATTCGCG), and d(CGCGAATTCACG). The 31P NMR signals of the dodecamer mismatch duplexes were assigned by 2D 1H/31P pure absorption phase constant time (PAC) heteronuclear correlation spectra. From the assigned H3' and H4' signals, the 31P signals of the base-pair mismatch dodecamers were identified. JH3'-P coupling constants for each of the phosphates of the dodecamers were obtained from 1H/31P J-resolved selective proton flip 2D spectra. By use of a modified Karplus relationship, the C4'-C3'-O3'-P torsional angles (epsilon) were obtained. JH3'-P coupling constants were measured for many of the oligonucleotides as a function of temperature. There exists a good linear correlation between 31P chemical shifts and the epsilon torsional angle. This correlation can be further extended to the C3'-O3'-P-O5' torsional angle (zeta) by using a linear relationship between epsilon and zeta obtained from crystal structure studies. The 31P chemical shifts follow the general observation that the more internally the phosphate is located within the oligonucleotide sequence, the more upfield the 31P resonance occurs. In addition, 31P chemical shifts show sequence- and site-specific variations. Analysis of the backbone torsional angle variations from the coupling constant analysis has provided additional information regarding the origin of these variations in 31P chemical shifts.

Base Sequence↗

PubMed1990

Subtypes of alpha 1-adrenoceptors in hippocampus of pigs, guinea-pigs, calves and humans: regional differences.

Radioligand binding studies were performed with membranes of guinea-pig, pig, calf and human hippocampus using [125I]BE 2254 (also known as [125I]HEAT) as the radioligand. [125I]BE 2254 bound with similar high affinity to saturable populations of recognition sites in all four membrane preparations. Competition curves obtained with a variety of ligands (e.g., WB 4101, benoxathian, 5-methyl-urapidil) were biphasic and the profiles of the high- and low-affinity components of [125I]BE 2254 binding were similar in all four membrane preparations. The data suggest that [125I]BE 2254 labels two subtypes of alpha 1-adrenoceptors in the hippocampus of these species. [3H]WB 4101 was used to label alpha 1A recognition sites in pig hippocampus membranes. [3H]WB 4101 recognized with high affinity an apparently homogeneous class of sites, as suggested by monophasic saturation and competition experiments. The rank order of affinity of the compounds for the high-affinity component of [125I]BE 2254 binding was similar to the rank order of affinity of these drugs for [3H]WB 4101 sites. The pharmacological profile of the low-affinity component of [125I]BE 2254 binding was similar to that described recently for the alpha 1B-adrenoceptor cloned from DDT1 cells. In autoradiographic studies with human hippocampal slices, CEC (chloroethylclonidine), an alkylating agent described to show selectivity for alpha 1B-adrenoceptors, displaced preferentially [125I]BE 2254 binding from the molecular layer of the dentate gyrus. In contrast, WB 4101 an alpha 1A-adrenoceptor-selective ligand, displaced preferentially [125I]BE 2254 binding in the hilus and the CA3 region. The data show that 2 subtypes of alpha 1-adrenergic recognition sites can be identified in the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗

PubMed1990

Binding characteristics of [125I]endothelin-1 in guinea-pig trachea and its displacement by endothelin-1, endothelin-3 and endothelin (16-21).

The presence of binding sites for endothelin-1 (ET-1) and endothelin-3 (ET-3) in airway epithelium, submucosa and smooth muscle of guinea-pig trachea was investigated using in vitro autoradiography. We also examined the ability of the C-terminal hexapeptide of endothelin, ET(16-21) to inhibit specific [125I]ET-1, binding. ET-1 appeared to bind to a single class of binding sites (nH not different from unity). In contrast, nH values for ET-3 displacement of [125I]ET-1 specific binding were different from unity, suggesting that these peptides bound to more than one site. ET (16-21) did not affect [125I]ET-1 binding. The present results suggest that the binding sites identified in guinea pig airway smooth muscle may be related to receptors mediating contractile responses to the endothelins.

Animals↗

PubMed1990

Urothelial grafts in mice.

Mouse bladder epithelium has been successfully transplanted to the bladders of syngeneic mice and has survived for at least twenty weeks. The fate of the transplanted tissue was followed using a fluorescein label. The recipient bladders were prepared by stripping the urothelium either by a surgical or a chemical method. The possibility of adopting a comparable technique for the treatment of early bladder cancer in man is discussed.

Animals↗

PubMed1990

Task demand and cardiovascular response magnitude: further evidence of the mediating role of success importance.

The interactive effects of success importance and task demand upon cardiovascular reactivity were investigated in 2 experiments. In Experiment 1, Ss learned that success on an easy or difficult memory task would allow them to avoid a mild or severe noise. As expected, pretask and task elevations in heart rate and systolic blood pressure increased with difficulty only when the noise was to be severe. In Experiment 2, Ss listened to a victim, attending either to how she must feel or to technical features of the presentation. Then they were given the chance to earn a donation by succeeding on an easy or difficult memory task. Pretask cardiovascular data accorded with predictions predicated on the assumption that the need to help would be greater among victim perspective Ss. For them, systolic elevations increased with difficulty, whereas for technical perspective Ss systolic elevations were low regardless of task demand.

Achievement↗

PubMed1990

Two-dimensional 1H and 31P NMR spectra and restrained molecular dynamics structure of an oligodeoxyribonucleotide duplex refined via a hybrid relaxation matrix procedure.

Assignment of the 1H and 31P resonances of a decamer DNA duplex, d(CGCTTAAGCG)2 was determined by two-dimensional COSY, NOESY and 1H-31P Pure Absorption phase Constant time (PAC) heteronuclear correlation spectroscopy. The solution structure of the decamer was calculated by an iterative hybrid relaxation matrix method combined with NOESY-distance restrained molecular dynamics. The distances from the 2D NOESY spectra were calculated from the relaxation rate matrix which were evaluated from a hybrid NOESY volume matrix comprising elements from the experiment and those calculated from an initial structure. The hybrid matrix-derived distances were then used in a restrained molecular dynamics procedure to obtain a new structure that better approximates the NOESY spectra. The resulting partially refined structure was then used to calculate an improved theoretical NOESY volume matrix which is once again merged with the experimental matrix until refinement is complete. JH3'-P coupling constants for each of the phosphates of the decamer were obtained from 1H-31P J-resolved selective proton flip 2D spectra. By using a modified Karplus relationship the C4'-C3'-O3'-P torsional angles (epsilon) were obtained. Comparison of the 31P chemical shifts and JH3'-P coupling constants of this sequence has allowed a greater insight into the various factors responsible for 31P chemical shift variations in oligonucleotides. It also provides an important probe of the sequence-dependent structural variation of the deoxyribose phosphate backbone of DNA in solution. These correlations are consistent with the hypothesis that changes in local helical structure perturb the deoxyribose phosphate backbone. The variation of the 31P chemical shift, and the degree of this variation from one base step to the next is proposed as a potential probe of local helical conformation within the DNA double helix. The pattern of calculated epsilon and zeta torsional angles from the restrained molecular dynamics refinement agrees quite well with the measured JH3'-P coupling constants. Thus, the local helical parameters determine the length of the phosphodiester backbone which in turn constrains the phosphate in various allowed conformations.

Absorption↗