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S R Turner

Publications and source records attributed to S R Turner.

At least 37 records · Page 2Linked to original sources
PubMed1995

Structure-based design of novel HIV protease inhibitors: carboxamide-containing 4-hydroxycoumarins and 4-hydroxy-2-pyrones as potent nonpeptidic inhibitors.

The low oral bioavailability and rapid biliary excretion of peptide-derived HIV protease inhibitors have limited their utility as potential therapeutic agents. Our broad screening program to discover nonpeptidic HIV protease inhibitors had previously identified compound II (phenprocoumon, K(i) = 1 muM) as a lead template. Crystal structures of HIV protease complexes containing the peptide-derived inhibitor I (1-(naphthoxyacetyl)-L-histidyl-5(S)-amino-6-cyclohexyl-3 (R),4(R)-dihydroxy-2(R)-isopropylhexanoyl-L-isoleucine N-(2-pyridylmethyl)amide) and nonpeptidic inhibitors, such as phenprocoumon (compound II), provided a rational basis for the structure-based design of more active analogues. This investigation reports on the important finding of a carboxamide functionally appropriately added to the 4-hydroxycoumarin and the 4-hydroxy-2-pyrone templates which resulted in a new promising series of nonpeptidic HIV protease inhibitors with improved enzyme-binding affinity. The most active diastereomer of the carboxamide-containing compound XXIV inhibited HIV-1 protease with a K(i) value of 0.0014 muM. This research provides a new design direction for the discovery of more potent HIV protease inhibitors as potential therapeutic agents for the treatment of HIV infection.

4-Hydroxycoumarins↗
PubMed1995

T-protein of the glycine decarboxylase multienzyme complex: evidence for partial similarity to formyltetrahydrofolate synthetase.

We have isolated and sequenced cDNA clones encoding T-protein of the glycine decarboxylase complex from three plant species, Flaveria pringlei, Solanum tuberosum and Pisum sativum. The predicted amino acid sequences of these clones are at least 87% identical and all are similar to the predicted sequences of the bovine, human, chicken and Escherichia coli T-proteins. Alignment of all these sequences revealed conserved domains, one of which showed a significant similarity to a part of the formyltetrahydrofolate synthetases from procaryotes and eucaryotes. This suggests that the T-protein sequence is not as unique as previously thought.

Amino Acid Oxidoreductases↗
PubMed1993

Inhibitors of the protease from human immunodeficiency virus: synthesis, enzyme inhibition, and antiviral activity of a series of compounds containing the dihydroxyethylene transition-state isostere.

A number of potential HIV protease inhibitory peptides that contain the dihydroxyethylene isostere were prepared and evaluated for their enzyme binding affinity and antiviral activity in cell cultures. From the template of a previously reported active peptide A, modifications at the N- and C-terminal groups were assessed for potential maintenance of good inhibitory activity of the resulting peptides. Among the active peptides found, peptide XVIII exhibited potent enzyme inhibitory activity. Interestingly, the previously reported, effective 1(S)-amino-2(R)-hydroxyindan C-terminal group for the preparation of very active HIV protease inhibitory peptides could not be applied to the template of peptide XVIII. Molecular modeling of peptide XVIII was studied using the X-ray crystal structure of peptide A as a starting point in order to study the likely conformation of peptide XVIII in the active-site cleft. Relative binding conformations of peptide A and XVIII were obtained, although the reason for poor binding affinity for a number of congeneric peptides in this report was not straightforwardly apparent. More importantly, however, peptide XVIII was found to exhibit more effective antiviral activity in the HIV-1/PBMC assay than the reference peptide A which was previously reported to be approximately equal in efficacy to the reverse transcriptase inhibitor AZT in this assay.

Animals↗
PubMed1993

The organisation and expression of the genes encoding the mitochondrial glycine decarboxylase complex and serine hydroxymethyltransferase in pea (Pisum sativum).

Restriction fragment length polymorphisms have been used to determine the chromosomal location of the genes encoding the glycine decarboxylase complex (GDC) and serine hydroxymethyltransferase (SHMT) of pea leaf mitochondria. The genes encoding the H subunit of GDC and the genes encoding SHMT both show linkage to the classical group I marker i. In addition, the genes for the P protein of GDC show linkage to the classic group I marker a. The genes for the L and T proteins of GDC are linked to one another and are probably situated on the satellite of chromosome 7. The mRNAs encoding the five polypeptides that make up GDC and SHMT are strongly induced when dark-grown etiolated pea seedlings are placed in the light. Similarly, when mature plants are placed in the dark for 48 h, the levels of both GDC protein and SHMT mRNAs decline dramatically and then are induced strongly when these plants are returned to the light. During both treatments a similar pattern of mRNA induction is observed, with the mRNA encoding the P protein of GDC being the most rapidly induced and the mRNA for the H protein the slowest. Whereas during the greening of etiolated seedlings the polypeptides of GDC and SHMT show patterns of accumulation similar to those of the corresponding mRNAs, very little change in the level of the polypeptides is seen when mature plants are placed in the dark and then re-exposed to the light.

Amino Acid Oxidoreductases↗
PubMed1992

Identification and localization of multiple forms of serine hydroxymethyltransferase in pea (Pisum sativum) and characterization of a cDNA encoding a mitochondrial isoform.

Serine hydroxymethyltransferase (SHMT) has been purified from the mitochondria of green pea leaves. Activity can be fractionated into two distinct peaks by ion exchange chromatography. While these two forms of the enzyme are immunologically indistinguishable, immunoinhibition experiments show the presence of a distinct non-mitochondrial third form of the enzyme to also be present in green pea leaves. While this mitochondrial form of SHMT is abundant in leaves it is absent from roots, although the two tissues have comparable SHMT activity. An antibody raised to purified mitochondrial SHMT was used to screen a cDNA expression library. The sequence of one of the isolated positive clones contained an open reading frame, which encoded a sequence that matched the amino acid sequence determined from the N terminus of the mature protein. The open reading frame encodes a mature protein of 487 amino acids with a M(r) of 54,000, together with a 27-31 amino acid serine-rich leader sequence, presumably required for mitochondrial targeting. The cDNA hybridizes to a small multigene family of 2-3 genes, which appear to be expressed predominantly in leaves. Comparison of the deduced amino acid sequence with the amino acid sequences of the rabbit mitochondrial and cytoplasmic SHMT, show that pea mitochondrial SHMT is equally similar to both of these enzymes. In addition, the rabbit sequences are more like one another than they are to the pea sequence, suggesting an interesting evolutionary relationship for these proteins.

Amino Acid Sequence↗
PubMed1992

Purification and primary amino acid sequence of the L subunit of glycine decarboxylase. Evidence for a single lipoamide dehydrogenase in plant mitochondria.

In order to purify the lipoamide dehydrogenase associated with the glycine decarboxylase complex of pea leaf mitochondria, the activity of free lipoamide dehydrogenase has been separated from those of the pyruvate and 2-oxoglutarate dehydrogenase complexes under conditions in which the glycine decarboxylase dissociates into its component subunits. This free lipoamide dehydrogenase which is normally associated with the glycine decarboxylase complex has been further purified and the N-terminal amino acid sequence determined. Positive cDNA clones isolated from both a pea leaf and embryo lambda gt11 expression library using an antibody raised against the purified lipoamide dehydrogenase proved to be the product of a single gene. The amino acid sequence deduced from the open reading frame included a sequence matching that determined directly from the N terminus of the mature protein. The deduced amino acid sequence shows good homology to the sequence of lipoamide dehydrogenase associated with the pyruvate dehydrogenase complex from Escherichia coli, yeast, and humans. The corresponding mRNA is strongly light-induced both in etiolated pea seedlings and in the leaves of mature plants following a period of darkness. The evidence suggests that the mitochondrial enzyme complexes: pyruvate dehydrogenase, 2-oxoglutarate dehydrogenase, and glycine decarboxylase all use the same lipoamide dehydrogenase subunit.

Amino Acid Oxidoreductases↗
PubMed1992

Cloning and characterization of the P subunit of glycine decarboxylase from pea (Pisum sativum).

A pea leaf cDNA library constructed in lambda gt11 was screened with an antibody raised to the P subunit of glycine decarboxylase. One of the positive clones isolated was sequenced and shown to contain an open reading frame, which encoded the entire P subunit polypeptide. Aligning the deduced amino acid sequence with the amino acid sequence determined directly from the NH2 terminus of the mature P subunit shows the presence of a putative 86 amino acid leader sequence, presumably required for import into the mitochondria, and gives a Mr of the mature protein of 105,000. Comparison of this deduced amino acid sequence with the sequence of a pyridoxal phosphate-containing peptide isolated from the P subunit of chicken liver glycine decarboxylase shows remarkable conservation. The P subunit, however, shows little sequence homology with other published amino acid decarboxylases. Expression of the P subunit mRNA shows a pattern very similar to that of the corresponding polypeptide: it is strongly light induced and is expressed at a much higher level in leaves than in other tissues. Southern blot analysis suggests that the P subunit is encoded by a small multigene family.

Amino Acid Oxidoreductases↗
PubMed1991

Renin inhibitory peptides. Incorporation of polar, hydrophilic end groups into an active renin inhibitory peptide template and their evaluation in a human renin infused rat model and in conscious sodium-depleted monkeys.

We previously reported that Boc-Pro-Phe-N-MeHis-Leu psi [CHOHCH2]-Ile-Amp (1) is a potent and specific inhibitor of human renin in vitro. It was shown to resist degradation by selected proteases and a rat liver homogenate. It was shown to inhibit plasma renin activity and to reduce blood pressure in renin-dependent-animal models both by the intravenous and by the oral routes using dilute citric acid as vehicle. In an effort to discover compounds with improved pharmacological efficacy, we set out to modify the physical characteristics of this highly lipophilic renin inhibitor by incorporation of hydrophilic end groups. We report here a variety of water-solubilizing groups and the resulting structure-activity relationship of these compounds. They all maintain an extremely high level of enzyme inhibitory activity in vitro. Evaluation of these potent renin inhibitors in a human renin infused rat model suggests that some of these compounds exhibit improved pharmacological efficacy in vivo. This observation was further confirmed in the conscious sodium-depleted cynomolgus monkey. Importantly, the oral efficacy was demonstrated in a water vehicle in the absence of citric acid.

Animals↗
PubMed1991

Conformationally constrained renin inhibitory peptides: cyclic (3-1)-1-(carboxymethyl)-L-prolyl-L-phenylalanyl-L-histidinamide as a conformational restriction at the P2-P4 tripeptide portion of the angiotensinogen template.

Interest in conformationally constrained peptides as potential inhibitors of renin led us to examine an N-terminal cycle of linear renin inhibitory peptides. A cyclic structure was prepared by joining the N-terminal proline at the P4 site to the imidazole ring of histidine at the P2 site via a carboxymethylene fragment. An efficient synthetic route to this 14-membered macrocycle was developed and this N-terminal cyclic tripeptide could be readily incorporated into renin inhibitory peptides. Monte Carlo molecular modeling methods were used to generate bound conformations of a representative inhibitor in a model of the renin active site, suggesting possible modes of binding of these inhibitors to renin. Two representative compounds that contain this 14-membered macrocycle were evaluated for their inhibitory activities against human plasma renin and they were found to exhibit very high binding affinity with IC50 values in the nanomolar and subnanomolar range.

Amino Acid Sequence↗
PubMed1991

Inhibitors of the protease from human immunodeficiency virus: design and modeling of a compound containing a dihydroxyethylene isostere insert with high binding affinity and effective antiviral activity.

The peptidomimetic template and the dihydroxyethylene isostere insert that were applied successfully to the design of renin inhibitors have been extended to the related protease from human immunodeficiency virus (HIV). The present report describes the structure-activity study leading to the identification of an inhibitor with a Ki of less than 1 nM for the HIV type-1 protease (compound II). This compound, containing a diol insert, is highly effective in blocking polyprotein processing in in vitro cell culture assays. Results obtained from kinetic analysis, studies of the stereochemistry of the insert, and modeling have led to insights as to the requisites involved in the active site-inhibitor interaction.

Amino Acid Sequence↗
PubMed1990

The effect of different alleles at the r locus on the synthesis of seed storage proteins in Pisum sativum.

Rocket immunoelectrophoresis was used to measure the accumulation of storage proteins in developing cotyledons of two Pisum sativum (pea) genotypes, that were close to isogenic except for the nature of the allele at the r locus. There was a marked decrease in legumin accumulation in the rr (wrinkled-seeded) genotype compared to the RR (round-seeded) genotype. The accumulation of vicilin did not differ greatly between the two genotypes. Pulse-labelling studies indicated that the differences in rates of accumulation of legumin between the rr and RR genotypes were a consequence of differences in rates of protein synthesis. Measurements of relative amounts of specific mRNAs, using cDNA clones as probes, showed lower amounts of legumin mRNA in developing cotyledons of the rr, compared to the RR, genotype. Both vicilin mRNAs and convicilin mRNA, the latter of which shows a similar temporal pattern of expression to those of the major legumin species, are relatively unaffected by the nature of the allele at the r locus. Nuclear run-on transcription experiments indicated no differences in the rate of synthesis of legumin transcripts in the rr and RR near-isolines. The consequences of homozygosity for the r allele on storage protein mRNA levels in vitro may be mimicked by manipulating the sucrose concentration of the culture medium.

Alleles↗
PubMed1990

Transcervical tubal embryo-stage transfer (TC-TEST).

Ultrasound-guided transcervical tubal cannulation (TC-TEST) was used to replace embryos to the fallopian tubes in 17 women whose fallopian tubes were inaccessible by the abdominal route but where at least one tube was shown to be freely patent on a preliminary hysterosalpingogram investigation. In two further cases, the fallopian tubes proved impossible to cannulate, and along with two instances where difficulty was experienced, a common underlying feature was an arcuate or septate configuration of the uterus. Three pregnancies ensued (17%) in cases where the procedure was free of difficulty and the transfers were demonstrably intratubal: two went to term and the third resulted in an ectopic pregnancy. The procedure has so far not shown a benefit over conventional IVF-ET and probably should be avoided in women with any type of tubal disorder.

Adult↗
PubMed1990

Renin inhibitory peptides. A beta-aspartyl residue as a replacement for the histidyl residue at the P-2 site.

In an effort to decrease the size and to increase the hydrophilicity of the previously prepared renin inhibitory peptides, it was postulated that one might be able to take advantage of the polar Thr-84 on the flap region of the enzyme renin by potential hydrogen bonding to polar functionality on the inhibitory peptide at the P-2 site. A beta-aspartyl residue with a carboxylic acid group was proposed to be a possible replacement for the histidyl residue at the P-2 site. A series of renin inhibitory peptides were prepared with the beta-aspartyl residue to probe the structure-activity relationship of the resulting peptides. Potent inhibitory peptides could be realized with activity in the subnanomolar range. Molecular modeling was also undertaken to investigate the interactions between the enzyme active site and the new inhibitors and to suggest a possible mode of binding of these ligands to the enzyme. From this modeling study, the role of Ser-229 at the active site in the bound conformer of the inhibitors was suggested. It was further noted in the analogue study that a malic acid residue, which is the oxygen analogue of the beta-aspartic acid residue, could lead to further enhancement of inhibitory potency of congeneric peptides. Small renin inhibitors, such as compound XII with molecular weight 535 and with no alpha-amino acid residue, could be prepared and exhibited renin inhibitory activity in the nanomolar range.

Aspartic Acid↗
PubMed1990

Neutrophil functional and arachidonic acid metabolic correlates and clinical disease activity in pirazolac-treated rheumatoid arthritis patients.

Neutrophils from 20 medication-free rheumatoid arthritis patients were chemotactically hyporesponsive to 2 x 10(-8) M formyl-methionyl-leucyl-phenylalanine (f-MLP) as compared to 20 normal controls. They were relatively high producers of 5-hydroxyeicosatetraenoic acid (5-HETE) and low producers of leukotriene C4 (LTC4). Neutrophils from 10 patients treated with pirazolac (4-(4-chlorophenyl)-1-(4-fluorophenyl)-5-pyrazole acetic acid) showed increased chemotactic responsiveness concomitantly with normalization of 5-HETE and LTC4 production and a decrease in the clinical parameters of disease activity. Clinically attainable (30-60 micrograms/ml) in-vitro doses of pirazolac further depressed the chemotactic responsiveness of normal neutrophils treated with 10(-5)M f-MLP. Effects on endothelial gating of migrating neutrophil populations may explain this apparent contradiction between in-vivo and in-vitro actions of pirazolac on neutrophil chemotaxis.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1989

Renin inhibitory peptides: a study of structural modifications in the peptide backbone.

We studied the peptide backbone modifications that improve the metabolic stability of the resulting peptides and yet retain high inhibitory activity against human plasma renin. A systematic investigation of N-alpha-methyl and C-alpha-methyl modifications at the P2 and P3 sites of renin-inhibitory peptides that contain part of the human angiotensinogen sequence led to the discovery of N-alpha-methyl amino acids at the P2 site as a useful structural modification. U-71,038 (11) inhibited human plasma renin with an in vitro potency (IC50) of 2.6 x 10(-10) mol/l. It is highly selective for renin and, as anticipated, resistant to proteolytic degradation. Additional study based on molecular graphic modelling has led us to propose a gamma-lactam conformational constraint at the P2-P3 site. This pseudo-dipeptide has proved useful in the preparation of active renin inhibitors. Compound 18a inhibited human plasma renin with an in vitro potency (IC50) of 2.1 x 10(-9) mol/l. This class of compounds also offers structural features for the study of enzyme-bound conformers.

Amino Acid Sequence↗
PubMed1988

Medroxyprogesterone acetate therapy in early pregnancy has no apparent fetal effects.

Medroxyprogesterone acetate (MPA; Provera) was given orally to 449 women from the 5th to 7th week of pregnancy until at least the 18th week. Data are recorded from two treatment groups (recurrent abortion and threatened abortion) and are compared to a matched series. A total of 1,016 pregnancies are included in the study, and all patients were recruited from a subfertile population conceiving from a range of infertility treatments. Early pregnancy wastage was high throughout the groups and was significantly elevated (43%; P less than .001) in those women who had vaginal bleeding in early pregnancy. The study focuses on the question of potential teratogenicity of progestagens administered in the first trimester. There were 15/366 (4.1%) infants with congenital abnormalities in the MPA-treated group and 15/428 in the untreated group (3.5%). The difference was not significant, and MPA is considered to have no embryopathic risk, nor is it likely to retain an abnormal fetus that might otherwise abort. It appears that MPA is a safe drug to use in pregnancy although the question of efficacy has not been addressed in this report. Considering other recent negative epidemiologic studies with regard to teratogenicity, we add to the conclusion that MPA cannot be demonstrated to have a measurable teratogenic risk and certainly does not present a risk for congenital heart disease and limb reduction defects.

Abnormalities, Drug-Induced↗
PubMed1988

Conformationally constrained renin inhibitory peptides: gamma-lactam-bridged dipeptide isostere as conformational restriction.

A model of the conformation of the enzyme-bound inhibitor of human renin suggested the possibility of a gamma-lactam conformational restriction at the P2-P3 site. Synthetic routes to these gamma-lactam dipeptide isosteres and their incorporation into potential renin inhibitors are described. Peptide VIa,b with a gamma-lactam conformational constraint and a hydroxyethylene isostere at the cleavage site inhibited human plasma renin with an IC50 value of 6.5 nM. The flexibility of these syntheses should make available a number of potential enzyme inhibitors with this structural feature for the study of enzyme-bound conformers.

Angiotensinogen↗