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A Rampersaud

Publications and source records attributed to A Rampersaud.

At least 19 recordsLinked to original sources
PubMed1998

Sphingolipids as receptor modulators. An overview.

Glycosphingolipids are amphipathic compounds that exist mainly in the plasmalemma with their oligosaccharide portion protruding into the extracellular environment. In this position they are admirably situated for interacting with both ligands and receptors. Binding studies have demonstrated that specific glycolipids function as receptors for some microorganisms and bacterial toxins. Specific oligosaccharides on both glycolipids and glycoproteins bind members of the selection families, and some gangliosides facilitate integrins binding to their ligands. Gangliosides modulate the trophic factor-stimulated dimerization, tyrosine phosphorylation, and subsequent signal transduction events of several tyrosine kinase receptors. GM3 inhibits both the epidermal growth factor receptor and basic fibroblast factor receptor; several gangliosides except GM3 inhibit the platelet-derived growth-factor receptor; GM1 enhances nerve growth-factor-stimulated activation of TrkA; insulin receptor is inhibited to varying degrees by several gangliosides, but 2-->3 sialosylparagloboside is most effective. Activities of the beta(1)-adrenergic and delta-opioid receptors are modulated by GM1. Available information suggests that glycolipids serve as coordinators of multiple receptor functions.

Animals↗
PubMed1994

The OmpR protein of Escherichia coli binds to sites in the ompF promoter region in a hierarchical manner determined by its degree of phosphorylation.

In Escherichia coli the ompF gene encodes a major outer membrane porin protein that is differentially regulated by the OmpR protein. OmpR acts as a positive as well as a negative regulator of ompF expression by binding to DNA sequences in the ompF promoter region. The DNA binding activity of OmpR is itself regulated by phosphorylation through the kinase protein EnvZ. Phosphorylation is believed to change the function of OmpR from an activator to a repressor molecule. By using purified OmpR and various regions of the ompF promoter we show that phosphorylation causes binding of OmpR to a DNA region between the -40 to -100 region of the ompF promoter previously shown to be important for ompF expression. As the amount of OmpR-phosphate increases, a binding site located at a further upstream -360 to -380 region was occupied. This latter site has been reported to be important for ompF repression. Further experiments indicate that the -70 to -100 region is a high affinity site, while the -45 to -60 and -360 to -380 regions are low affinity sites. We also provide evidence that OmpR binding at the -360 to -380 region requires previous binding at downstream sequences, which is indicative of long range interactions between OmpR molecules. We interpret our results in terms of a model for ompF regulation involving hierarchical binding by phosphorylated OmpR and potential DNA looping.

Bacterial Outer Membrane Proteins↗
PubMed1993

Phenotypic revertant mutations of a new OmpR2 mutant (V203Q) of Escherichia coli lie in the envZ gene, which encodes the OmpR kinase.

The Escherichia coli ompR2 allele ompR472 contains a valine-to-methionine point mutation at position 203, resulting in an OmpF-constitutive OmpC- outer membrane phenotype. In the present study, OmpR residue V-203 was replaced with glutamine (V203Q mutation), resulting in the same outer membrane phenotype. However, unlike the OmpFc OmpC- phenotype conferred by the OmpR(V203M) mutant protein, the OmpFc OmpC- phenotype produced by the OmpR(V203Q) mutation was suppressed by the envZ11(T247R) allele. Additional suppressors of OmpR(V203Q) were isolated by random mutagenesis. All suppressor mutations were found in the envZ gene and conferred an OmpC+ OmpF- phenotype in the presence of the wild-type ompR. These envZ11-like mutations mapped to a region different from those previously reported and were incapable of suppressing the ompR(V203M) allele. Our results indicate that while methionine or glutamine replacements could cause similar effects on OmpF and OmpC expression, they conferred different abilities on the mutant proteins to be suppressed by envZ.

Bacterial Outer Membrane Proteins↗
PubMed1992

Observations on the synthesis and in vivo photodynamic activity of some benzochlorins.

An improved synthesis of benzochlorins is reported. Demetallation of the meso-hydroxymethylvinyl derivative of octaethylporphyrin, followed by treatment with sulfuric acid results in cyclization to generate the corresponding octaethylbenzochlorin in high yield. Prolonged treatment with acid generates the sulfonated derivative. These sensitizers were shown to be efficient photodynamic agents in vivo. Animals bearing a transplanted N-[4-(5-nitro-2-furyl)-2-thiazoly]formamide induced urothelial tumor were treated with either the benzochlorin or its sulfonated derivative. Irradiation of tumors 24 h later resulted in a significant tumoricidal effect in a short term assay. We conclude that benzochlorins warrant further examination as potential agents for use in photodynamic therapy.

Animals↗
PubMed1992

Null phenotype for cytochrome P450 2B2 in the rat results from a deletion of its structural gene.

The absence of phenobarbital (PB)-inducible cytochrome P450 2B2 (CYP2B2) in hepatic microsomes from Marshall 520 (M520) and Wistar Munich (WM) inbred strains of rat was previously reported [Biochem. Genet. 25:527-534 (1987)], and it was subsequently shown for M520 rats that corresponding CYP2B2 mRNA was not detected in hepatic extracts from either control or PB-treated animals [DNA 8:29-37 (1989)]. In the present study, solution hybridization was used to quantify PB-induced CYP2B2 and CYP2B1 mRNAs in livers from M520, WM, and outbred Sprague-Dawley rats, as well as additional inbred strains that express all known electrophoretic phenotypes for both of these closely related isozymes. Amounts of these mRNAs were also measured for F1 and F2 progenies of crosses involving M520 rats. The results indicated that the extent of PB induction of both isozymes appears to be independent of the electrophoretic phenotype. It was also shown that the null phenotype for CYP2B2 observed in M520 rats results from a mutation of a single autosomal gene and is inherited codominantly, regarding protein and mRNA phenotypes. Analyses of restriction digests and specific polymerase chain reaction products of hepatic DNAs revealed that the basis for the null phenotype of CYP2B2 in M520 and WM rats was a deletion of the CYP2B2 gene.

Alleles↗
PubMed1991

Ca2(+)-enhanced phosphorylation of a chimeric protein kinase involved with bacterial signal transduction.

The Tar-EnvZ hybrid molecule (Taz1) is an inner membrane transducer that activates OmpR, a transcriptional activator for porin gene expression (ompC), in response to an aspartic acid signal. Signal transduction by Taz1 most likely involves a phosphorylated Taz1 intermediate that donates its phosphate to OmpR. Phosphorylated OmpR has already been implicated in transcriptional activation of porin genes. Using a cell-free system containing Taz1-enriched membrane fractions, we have examined the phosphorylation properties of Taz1 and the stimulatory effects of divalent and monovalent ions. Highest activation of Taz1 phosphorylation was observed with CaCl2, and its stimulation could be observed with as low as 60 microM of CaCl2. Phosphorylated Taz1 could readily donate its phosphate group to OmpR in the presence of calcium. CaCl2 was also able to enhance phosphorylation of intact membrane-bound EnvZ and a cytoplasmic fragment of EnvZ lacking the receptor and transmembrane domains. These results indicate that the site for CaCl2 stimulation is within the cytoplasmic region of EnvZ and probably involves an enhanced rate of EnvZ phosphorylation.

Autoradiography↗
PubMed1991

Characterization of distinct angiotensin II binding sites in rat adrenal gland and bovine cerebellum using selective nonpeptide antagonists.

We investigated the characteristics of 125I-AII binding to rat adrenal and bovine cerebellar membranes in the presence and absence of new nonpeptide angiotensin II (AII) receptor ligands. The imidazole AII ligands, DUP753 and WL19, both produced biphasic competition curves to 125I-AII binding in rat adrenal glomerulosa and adrenal medulla particles, suggesting the existence of two distinct AII binding sites. Antagonist affinity (Ki) and binding capacity (Bmax) for each binding site was determined using nonlinear analysis of competition data fit to a two-site model. The high capacity site (68% of total specific 125I-AII bound) in glomerulosa had high affinity for DUP753 (4.6 +/- 0.8 nM) and low affinity for WL19 (29 +/- 3 microM), and the low capacity site had high affinity for WL19 (3.3 +/- 1.4 nM) and low affinity for DUP753 (51 +/- 9 microM). Conversely, in medulla, the high capacity site (77% total binding) had high affinity for WL19 (19 +/- 6 nM) and low affinity for DUP753 (29 +/- 8 microM), and the low capacity site had low affinity for WL19 (25 +/- 7 microM) but a high affinity for DUP753 (2.8 +/- 2.0 nM). In glomerulosa, binding parameters for the nonpeptide ligands at each site derived from monophasic competition curves obtained in the presence of either 0.3 microM DUP753 or WL19 to selectively block the high or low capacity binding site, respectively, were similar to values determined from the biphasic competition curves. Unlike the nonpeptide inhibitors, unlabeled AII yielded monophasic inhibition curves.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1991

Procaine, a local anesthetic, signals through the EnvZ receptor to change the DNA binding affinity of the transcriptional activator protein OmpR.

Local anesthetics are known to reduce the level of OmpF and increase the synthesis of OmpC in the outer membrane of Escherichia coli K-12. It has been shown that the anesthetics procaine and phenethyl alcohol (PEA) act at the transcriptional level for ompF and ompC and that in the case of procaine, its action is dependent on EnvZ, the membrane-bound signal transducer required for ompF and ompC expression. In an effort to further understand how anesthetics regulate ompF and ompC expression, we have analyzed the DNA binding properties of OmpR (the transcriptional activator protein for ompF and ompC genes) from cells treated with procaine or PEA. Treatment of a wild-type cell with either anesthetic converted OmpR from a low-affinity DNA binding form to a high-affinity DNA binding form. The change in DNA binding affinity was correlated with alterations in outer membrane porin profiles and could occur in the absence of protein synthesis. A strain lacking EnvZ was unable to respond to procaine to produce either the shift in the OmpR DNA binding property or cause any change in the outer membrane porin profile. PEA treatment was also dependent on EnvZ for the alteration in the OmpR DNA binding property, but it could induce ompC expression in the absence of EnvZ. Further studies suggest that the amino-terminal region of EnvZ is responsible for the procaine signalling. Our results indicate that procaine and PEA regulate ompF and ompC expression by modifying the DNA binding properties of OmpR through EnvZ signal transduction.

Bacterial Outer Membrane Proteins↗
PubMed1990

In vivo phosphorylation of OmpR, the transcription activator of the ompF and ompC genes in Escherichia coli.

An in vivo approach was taken to assess whether the phosphorylated state of the transcription activator OmpR was affected by changes in the osmolarity of the growth medium or by mutations in envZ, the gene encoding the inner membrane histidine kinase that phosphorylates OmpR. We present results that support the view that increased phosphorylation of OmpR is correlated with enhanced expression of ompC. The in vivo phosphorylation approach was also used to show that OmpR can be phosphorylated in an envZ null strain. This result indicates that phosphorylation cross talk can occur in vivo between OmpR and a kinase(s) that is functionally homologous to envZ.

Bacterial Outer Membrane Proteins↗
PubMed1989

Characterization of OmpR binding sequences in the upstream region of the ompF promoter essential for transcriptional activation.

In Escherichia coli the expression of the outer membrane porin gene ompF requires the transcriptional activator protein OmpR. Previous DNase I footprinting experiments with purified OmpR localized the OmpR binding site from positions -105 to -60 (relative to the transcriptional start site) in the ompF promoter, and three tandem 10-base pair sequences elements (Fa, Fb, and Fc) within this region were proposed to be important for OmpR recognition. In order to elucidate the roles of the F boxes for transcriptional activation of ompF, various F box deletions and point mutations were constructed and analyzed for their effects on ompF-lacZ expression and OmpR binding. Removal of 102 nucleotides, which included a portion of the OmpR binding region (the Fa box), evidenced the largest decrease in transcriptional activation and significantly reduced OmpR binding. Additional deletion of four more base pairs in this target site (representing half of the Fb box) further reduced ompF expression. OmpR interactions with DNA sequences representing the OmpR binding region were analyzed by DNA mobility shift experiments. A 43-base pair ompF oligonucleotide containing the Fa, Fb, and Fc regions was sufficient for OmpR-dependent DNA binding using either purified OmpR or cell supernatants. The central C residue in each F box was changed to a T and unique patterns of protein-DNA complexes were observed that were different from that of the wild type binding site. The most dramatic effect on OmpR binding was observed when the C to T transversion occurred in the Fb box, and this mutation also reduced the level of ompF-lacZ expression. Our results indicate that the F boxes play important roles in the activation of ompF expression, and we suggest that OmpR may interact cooperatively with these boxes.

Bacterial Outer Membrane Proteins↗
PubMed1989

Activation of bacterial porin gene expression by a chimeric signal transducer in response to aspartate.

The Tar chemoreceptor of Escherichia coli is a membrane-bound sensory protein that facilitates bacterial chemotaxis in response to aspartate. The EnvZ molecule has a membrane topology similar to Tar and is a putative osmosensor that is required for osmoregulation of the genes for the major outer membrane porin proteins, OmpF and OmpC. The cytoplasmic signaling domain of Tar was replaced with the carboxyl portion of EnvZ, and the resulting chimeric receptor activated transcription of the ompC gene in response to aspartate. The activation of ompC by the chimeric receptor was absolutely dependent on OmpR, a transcriptional activator for ompF and ompC.

Aspartic Acid↗
PubMed1989

New sensitizers for photodynamic therapy: controlled synthesis of purpurins and their effect on normal tissue.

Purpurins are a class of porphyrin derivative that have been shown to have good in vivo cytotoxicity to N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) induced rat bladder tumors (AY-27) implanted into Fisher 344 rats. The synthesis of purpurins from etioporphyrin I and coproporphyrin I proceeds in high yield and with a high degree of regioselectivity. Product formation can be rationalized in terms of relief of steric strain about the periphery of the purpurin macrocycle. The effect of therapeutic light doses using the rat footpad model suggests that, at therapeutic sensitizer doses, normal tissue damage is within acceptable limits, particularly for metalated purpurins.

Animals↗
PubMed1987

Mapping of genes for cytochromes P-450b, P-450e, P-450g, and P-450h in the rat. Demonstration of two gene clusters with P450-b,e localized on chromosome 1.

Inbred ACI, WF, and RCS rats having characteristic markers for albino (c), hemoglobin beta-chain (Hbb), and pink-eyed dilution (p) on chromosome 1 and expressing variants for hepatic cytochromes P-450b, P-450e, P-450g, and P-450h were used in genetic mapping studies for these hemoproteins. The results of WF X (ACI X WF)F1 and RCS X (WF X RCS)F1 backcrosses revealed the existence of two gene clusters designated the P450-b,e and P450-g,h loci. The linkage map P450-b,e-p-c-Hbb on rat chromosome 1 was demonstrated and found to be congruent with Coh(P450-b,e)-p-c-Hbb on mouse chromosome 7. P450-g,h is not linked with P450-b,e and the other markers tested on rat chromosome 1. It appears that close genetic linkage, rather than common functional/regulatory properties, typify members of cytochrome P-450 families/subfamilies.

Animals↗
PubMed1987

Polymorphisms of four hepatic cytochromes P-450 in twenty-eight inbred strains of rat.

Two-dimensional gel electrophoresis of hepatic microsomes from phenobarbital-treated animals was used to analyze electrophoretic/regulatory polymorphisms for cytochromes P-450b, P-450e, P-450g, and P-450h in 28 inbred strains of rat. Previous studies with outbred rats revealed the existence of four electrophoretic variants for P-450b, two for P-450e, and three for P-450h as well as two regulatory alleles for P-450g. With the exception of one allozymic form of P-450h, all of these alleles as well as a novel (null) allele for P-450e were found to be homozygous in at least two of the inbred strains tested. Eight phenotypes for combinations of these four cytochromes P-450 were observed. Inbred strains were identified that can be used in studies on the structure/function of unique cytochrome P-450-allozymes and in genetic crosses to map the four distinct cytochrome P-450 genes.

Alleles↗
PubMed1987

A regulatory polymorphism for rat hepatic cytochrome P-450g.

Rat hepatic cytochrome P-450g is a male-specific hemoprotein found at significant levels only in adult animals. In the present study, two-dimensional gel electrophoretic and immunochemical methods were used to study a polymorphism of this isozyme and its ontogenetic regulation. Inbred ACI/Hsd and WF/Hsd rats were found to express high and low levels of cytochrome P-450g, respectively. F1 hybrids of these strains showed additive inheritance for this trait and the responsible gene was found to be autosomal. Cytochrome P-450g and another male-specific form of the enzyme, cytochrome P-450h, were characterized by a similar time-course for their ontogenetic expressions. However, unlike cytochrome P-450g, the level of cytochrome P-450h was indistinguishable in hepatic microsomes from mature ACI/Hsd and WF/Hsd rats. Considering these results, we tentatively conclude that the gene regulating the level of cytochrome P-450g is Cis-acting.

Aging↗
PubMed1986

Cytochrome P-450 polypeptides in pulmonary microsomes from rats.

Pulmonary microsomal polypeptides from different strains of rats were resolved using two-dimensional electrophoresis and were further characterized by in situ peptide mapping. Triton X-114 detergent separation was used to enrich cytochromes P-450 (P-450) and other integral membrane proteins from pulmonary microsomes, and these were directly compared with corresponding polypeptides from hepatic microsomes. The results demonstrated that P-450b and epoxide hydrolase were present in the lungs of male and female rats and that their expression in this tissue was independent of phenobarbital treatment. P-450e, which is co-induced with P-450b in the liver, was not detected in pulmonary microsomes under any condition. Four other pulmonary microsomal polypeptides were characterized and preliminary evidence suggested that they represent unique isozymic forms of P-450 with three of them being related to P-450b.

Animals↗
PubMed1985

Microheterogeneity of a male-specific rat hepatic cytochrome P-450: existence of three allozymic forms.

Preparations of hepatic cytochrome P-450 h [D. E. Ryan, et al. (1984) J. Biol. Chem. 259, 1239] and cytochrome P-450 2c [D. J. Waxman (1984) J. Biol. Chem. 259, 15481] from outbred Sprague-Dawley rats were analyzed using two-dimensional electrophoresis and in situ peptide mapping. Both preparations consisted of the same isozyme which was previously characterized as a developmentally regulated, male-specific cytochrome P-450 active in the 16 alpha-hydroxylation of steroids. Each preparation evidenced microheterogeneity which was shown, in part, to result from the existence of two genetically determined variant forms of cytochrome P-450 h/2c. Analyses of hepatic microsomes from several inbred strains of rat revealed that each was characterized by a single variant form of this isozyme, with some strains expressing a variant that was not present in Sprague-Dawley rats. Genetic crosses indicated that these electrophoretic variants represent allozymic forms of cytochrome P-450 h/2c which are codominantly expressed at a single autosomal locus. Additional microheterogeneity of each allozymic form of cytochrome P-450 h/2c was shown to result from a specific in vitro modification that may involve limited proteolysis near its C terminus by a microsome-bound protease.

Alleles↗