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Biomedical subjects

S Kumar

Publications and source records attributed to S Kumar.

At least 1,495 records · Page 83Linked to original sources
PubMed1992

Serologic diagnosis of viral hepatitis.

Serologic tests are the most accurate method of identifying a viral cause for a liver disorder and distinguishing between the different forms of viral hepatitis. Although such characteristics of viral hepatitis as route of transmission and incubation period may be helpful in differential diagnosis, they seldom are sufficient to make an exact diagnosis. Laboratory tests or liver biopsy may help to differentiate liver disorders but again usually do not identify the form of viral hepatitis that is present. However, liver biopsy is often of value in patients with chronic hepatitis to determine the severity of disease, aid in prognosis, and, in some cases, serve as a guide to antiviral therapy.

Diagnosis, Differential↗
PubMed1992

Immunization with soluble protein-pulsed spleen cells induces class I-restricted cytotoxic T lymphocytes that recognize immunodominant epitopic peptides from Plasmodium falciparum and HIV-1.

CTL lines specific for two different proteins derived from the human pathogens, Plasmodium falciparum (malaria) circumsporozoite protein and HIV-1 reverse transcriptase, were obtained by immunizing mice with protein-pulsed syngeneic spleen cells. The lysis of the target cells was dependent on a class I MHC molecule and the accessory molecule CD8. Immunodominant epitopic peptides were identified previously in the two proteins using murine CTL derived after immunization with recombinant virus or sporozoites, or using CTL from HIV-1-infected patients. These peptides were also recognized by the CTL lines obtained after protein-pulsed spleen-cell immunization. A new CTL antigenic determinant was localized in HIV-1 reverse transcriptase to residues 514 to 528, a sequence that, if folded as an alpha-helix, would be strongly amphipathic. The determinant was tentatively narrowed, using overlapping peptides, to a core of at least nine residues, 515 to 523. This site was also recognized by CTL obtained by the two different methods of immunization. Therefore, extracellular proteins incubated with spleen cells can be processed and presented in vivo in the same way as intracellular proteins, resulting in recognition of the same epitopes in association with the same class I MHC molecules. The potential implications for vaccine development and for the understanding of class I-restricted Ag presentation are discussed.

Amino Acid Sequence↗
PubMed1992

The NH2 terminus of retinal recoverin is acylated by a small family of fatty acids.

Recoverin is a recently identified Ca(2+)-binding protein that imparts Ca2+ sensitivity to vertebrate photoreceptor guanylate cyclase. In response to photo-induced depletion of intracellular cGMP and Ca2+, recoverin stimulates resynthesis of cGMP. Bovine retinal recoverin has now been analyzed by electrospray mass spectrometry (ESI-MS) for post-translational modifications that might influence its activity. Heterogeneous acylation was detected at the NH2 terminus of bovine retinal recoverin. The NH2-terminal glycine of each retinal recoverin molecule is linked to one of four different types of acyl groups. The most abundant is myristoleate (14:1), but 14:0, 14:2, and 12:0 acyl residues are also present.

Acylation↗
PubMed1992

A 1H-NMR study of the DNA binding characteristics of thioformyldistamycin, an amide isosteric lexitropsin.

The interaction of thioformyldistamycin, an amide isostere of the naturally occurring antibiotic distamycin A, with a self-complementary decadeoxynucleotide duplex, d(CGCAATTGCG)2, has been examined using a variety of high-field 1H-NMR techniques. The ligand exhibits two forms in solution arising from geometric isomerism due to restricted rotation around the thioformamide bond. Only the thermodynamically more stable Z-form is shown to bind to the oligonucleotide along its minor groove at the central 5'-AATT segment with the end groups of the ligand extending into the flanking GC regions but without any close contact at the amidinium terminus. Cross-peaks involving characteristic intra- and interresidue proton connectivities in the 2D experiments (COSY and NOESY) were employed to assign individual resonances of both strands in the asymmetric DNA-drug complex. The solution structure of the complex was constructed by molecular mechanics calculations based upon initial estimates of drug-DNA NOE contacts and further refined through energy minimization. These results complement previous structural studies on distamycin and other lexitropsins with oligonucleotides. The exchange of the ligand between two equivalent binding sites on the DNA sequence was estimated to occur at 40 s-1 with a free energy of activation of 16.5 kcal.mol-1 at 321-326 K. There was no evidence of formation of a 2:1 drug-oligomer complex, in contrast to the case of the natural product, which is attributed to steric demands of the larger sulfur atom.

Base Sequence↗
PubMed1992

Selenite is a substrate for calf thymus thioredoxin reductase and thioredoxin and elicits a large non-stoichiometric oxidation of NADPH in the presence of oxygen.

The thioredoxin system, comprising NADPH, thioredoxin reductase and thioredoxin reduces protein disulfides via redox-active dithiols. We have discovered that sodium selenite is a substrate for the thioredoxin system; 10 microM selenite plus 0.05 microM calf thymus thioredoxin reductase at pH 7.5 caused a non-stoichiometric oxidation of NADPH (100 microM after 30 min). In contrast, thioredoxin reductase from Escherichia coli showed no direct reaction with selenite, but addition of 3 microM E. coli thioredoxin also resulted in non-stoichiometric oxidation of NADPH, consistent with oxidation of the two active-site thiol groups in thioredoxin to a disulfide. Kinetically, the reaction was complex with a lag phase at low selenite concentrations. Under anaerobic conditions the reaction stopped after 1 mol selenite had oxidized 3 mol NADPH; the admission of air then resulted in continued consumption of NADPH consistent with autooxidation of selenium intermediate(s). Ferricytochrome c was effectively reduced by calf thymus thioredoxin reductase and selenite in the presence of oxygen. Selenite caused a strong dose-dependent inhibition of the formation of thiol groups from insulin disulfides with either the E. coli or calf-thymus thioredoxin system. Thus, under aerobic conditions selenite catalyzed, NADPH-dependent redox cycling with oxygen, a large oxygen-dependent consumption of NADPH and oxidation of reduced thioredoxin inhibiting its disulfide-reductase activity.

Anaerobiosis↗
PubMed1992

Identification of a set of genes with developmentally down-regulated expression in the mouse brain.

Using a subtraction cloning approach, we have isolated a set of cDNA clones from mouse neural precursor cells whose respective mRNA levels are down-regulated during the development of mouse brain. Single stranded DNA prepared from neuronal precursor cell cDNA library in lambda Zap vector was subtracted with poly (A)+ RNA prepared from postnatal and adult mouse brain to obtain several clones which show developmental down-regulation of expression. Their patterns of expression indicate that these genes may play important roles during the embryonic development and differentiation of central nervous system.

Aging↗
PubMed1992

Pro-opiomelanocortin synthesized by corticotrophs bears asparagine-linked oligosaccharides terminating with SO4-4GalNAc beta 1,4GlcNAc beta 1,2Man alpha.

We have determined that greater than or equal to 80% of the Asn-linked oligosaccharides on the glycosylated form of mouse adrenocorticotropin (15-kDa adrenocorticotropin (ACTH)) bear one or more branches terminating with the sequence SO4-4GalNAc beta 1,4GlcNAc beta 1,2Man alpha (S4GGnM). Proopiomelanocortin (POMC), the precursor of ACTH, is the first example of a glycoprotein that is not a member of the glycoprotein hormone family to bear such sulfated structures. Like lutropin and thyrotropin, 15-kDa ACTH bears dibranched oligosaccharides terminating with SO4-4-GalNAc; however, at least half of the oligosaccharides on 15-kDa ACTH terminating with SO4-4-GalNAc consist of more highly branched structures that have not previously been described. Both the GalNAc beta 1,4GlcNAc beta 1,2Man-4-sulfotransferase and the glycoprotein hormone-specific GalNAc-transferase are expressed in the corticotroph-derived AtT-20 cell line. A tripeptide recognition sequence, Pro-Val-Lys, similar to the Pro-Leu-Arg sequence required for recognition of glycoprotein hormone alpha- and beta-subunits by the glycoprotein hormone-specific GalNAc-transferase, is present 8 residues amino-terminal to the glycosylated Asn of 15-kDa ACTH. Thus, POMC has the features expected for specific addition of the S4GGnM sequence to its oligosaccharides. The recent discovery of a receptor in hepatic endothelial cells that recognizes oligosaccharides terminating with S4GGnM suggests these sulfated oligosaccharides will regulate the circulatory half-life of glycosylated POMC cleavage products.

Amino Acid Sequence↗
PubMed1992

Genotoxic effect of smoke-dried meat extract in Swiss albino mice using sperm head shape abnormality test.

The genotoxic effect of an extract of smoke-dried meat was assayed by employing in vivo sperm head shape abnormality. A significant dose responsive mutagenic effect was observed using the sperm head shape abnormality test. The result indicates that higher doses i.e., 100 and 200 mg/kg body wt. of smoke meat extract, significantly induced sperm head shape abnormality as compared to lower doses i.e., 20 mg/kg body wt. and control.

Animals↗
PubMed1992

Expression of interleukin 1-inducible genes and production of interleukin 1 by aging human fibroblasts.

The interleukin 1 (IL-1)-inducible mRNAs for plasminogen activator inhibitor type 2, manganese superoxide dismutase, and urokinase are overexpressed in old (greater than 70% of life-span completed) but not in young (less than 40% of life-span completed) human foreskin fibroblasts. Furthermore, the activity of this superoxide dismutase is greater in old than in young fibroblasts. IL-1 beta mRNA is detected by Northern blot analysis in old fibroblasts and its expression is further enhanced by a treatment with IL-1 alpha. IL-1 alpha and IL-1 beta mRNAs are detected in old foreskin and lung fibroblasts by a sensitive reverse transcription-PCR assay. IL-1 mRNA is consistently expressed after fibroblasts have completed 85% of their in vitro life-span; an assay with specific antibodies shows that IL-1 alpha is present in these fibroblasts. Prolonged treatment with IL-1 receptor antagonist decreases the levels of IL-1 alpha and of IL-1 alpha and IL-1 beta mRNAs. This observation suggests that IL-1 receptor antagonist inhibits an autocrine loop responsible for IL-1 expression. IL-1 mRNA accumulates in young fibroblasts treated with cycloheximide, suggesting that it is transcribed but unstable in these cells; accumulation of IL-1 mRNA in old fibroblasts may be due at least in part to increased stability. IL-1 alpha stimulates DNA synthesis in young fibroblasts but has progressively less effect as the cells age in culture. These data indicate that IL-1 is "constitutively" produced by aging fibroblasts and that IL-1 induces the expression of specific proteins in these cells. The mechanism for this constitutive production of IL-1 is explored in this paper.

Base Sequence↗
PubMed1992

Selenodiglutathione is a highly efficient oxidant of reduced thioredoxin and a substrate for mammalian thioredoxin reductase.

Selenium compounds like selenite (SeO3(2-) may form a covalent adduct with glutathione (GSH) in the form of selenodiglutathione (GS-Se-SG), which is assumed to be important in the metabolism of selenium. We have isolated GS-Se-SG and studied its reactions with NADPH and thioredoxin reductase from calf thymus or with thioredoxin reductase and thioredoxin from Escherichia coli. Incubation of 0.1 microM calf thymus thioredoxin reductase or 0.1 microM thioredoxin reductase and 1 microM thioredoxin from E. coli with 5, 10, or 20 microM GS-Se-SG resulted in a fast initial reaction, followed by a large and continued oxidation of NADPH. However, anaerobic incubation of 0.1 microM calf thymus thioredoxin reductase and 20 microM GS-Se-SG resulted only in oxidation of a stoichiometric amount of NADPH; admission of oxygen started continuous NADPH oxidation. Contrary to the mammalian enzyme, GS-Se-SG was not a substrate for thioredoxin reductase from E. coli. The rate of the oxygen-dependent reaction between calf thymus thioredoxin reductase and GS-Se-SG was increased 2-fold in the presence of 4 mM GSH, indicating that HSe- was the reactive intermediate. Glutathione reductase from rat liver reduced GS-Se-SG with a very slow continued oxidation of NADPH, and the presence of the enzyme did not affect the oxygen-dependent nonstoichiometric oxidation of NADPH by GS-Se-SG and thioredoxin reductase. Fluorescence spectroscopy showed GS-Se-SG to be a very efficient oxidant of reduced thioredoxin from E. coli and kinetically superior to insulin disulfides. Thioredoxin-dependent reduction of CDP to dCDP by ribonucleotide reductase was effectively inhibited by GS-Se-SG.

Animals↗
PubMed1992

Recognition of specific DNA sequences by mitomycin C for alkylation.

Synthetic oligodeoxyribonucleotides were reacted with mitomycin C (MC) under conditions which restricted MC to monofunctional alkylating activity. The yields of monofunctional alkylation of oligonucleotides with variable sequence were determined by enzymatic digestion of the reaction mixture to unreacted nucleosides and the product of alkylation, a MC-deoxyguanosine adduct (2), followed by quantitative analysis by HPLC. The relative yields of 2 reflected relative monoalkylation reactivities. They were compared in a series of oligonucleotides having the sequence 5'-NGN' in which the 5'-base was varied while the 3'-base was kept constant as T. Under Na2S2O4 activation conditions a striking enhancement of the yield was observed at the 5'-CG sequence: 36%, compared to 2% at 5'-AG and 4.1% at 5'-TG. The 5'-GG sequence also showed enhanced reactivity although to a lesser extent (14.7%). The enhancements were specific to the duplex state of the oligonucleotides. Using NADPH:cytochrome c reductase as the reducing agent gave similar results. MC activated by acidic pH also displayed 5'-CG alkylation specificity. 10-Decarbamoyl-MC activated by Na2S2O4 showed the same 5'-CG specificity as MC. Replacement of deoxyguanosine by deoxyinosine in the opposite strand at a 5'-CG site abolished the enhancement of alkylation. Such replacement at a 5'-GG site had a similar effect. It was found that the base 3' to the guanine had only a relatively modest modulating effect on the enhanced reactivity of the G at the 5'-CG sequence. This 3'-base effect appeared to be independent of the 5'-base of the 5'-NGN' triplet. The order of reactivity is 3'-(C greater than T greater than A).(ABSTRACT TRUNCATED AT 250 WORDS)

Alkylating Agents↗