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D Sarkar

Publications and source records attributed to D Sarkar.

At least 73 records · Page 4Linked to original sources
PubMed1995

Partial purification and characterization of a soluble protein phosphatase from Leishmania donovani promastigotes.

A soluble protein phosphatase from the promastigote form of the parasitic protozoan Leishmania donovani was partially purified using Sephadex G-100, DEAE-cellulose and again Sephadex G-100 columns. The partially purified enzyme showed a native molecular weight of about 42,000 in both Sephadex G-100 and sucrose density gradient centrifugation. The sedimentation constant, stokes radius and frictional ratio were found to be 3.43S, 2.8 nm and 1.20 respectively. The enzyme preferentially utilized phosphohistone as the best exogenous substrate. Mg2+ ions were essential for enzyme activity; among other metal ions Mn2+ can replace Mg2+ to a certain extent whereas Ca2+, Co2+ and Zn2+ could not substitute for Mg2+. The pH optimum of the enzyme was 6.5-7.5 and the temperature optimum 37 degrees C. The apparent Km for phosphohistone was 7.14 microM. ATP, ADP, inorganic phosphate and pyrophosphate had inhibitory effect on the enzyme activity whereas no inhibition was observed with sodium tartrate and okadaic acid. These results suggest that L. donovani promastigotes possess a protein phosphatase which has similar characteristics with the mammalian protein phosphatase 2C.

Animals↗
PubMed1995

Recent kala-azar cases in India: isozyme profiles of Leishmania parasites.

In this study, three WHO recommended reference strains of Leishmania donovani (DD8), L. tropica (K27) and L. major (5 ASKH) were compared by isozyme analysis of 9 soluble enzymes using cellulose acetate electrophoresis (CAE). The isozyme profile of the three species showed distinct electrophoretic mobilities of the enzymes studied. This technique was applied to study the enzyme patterns of 8 clinical isolates of visceral leishmaniasis (VL) and two post kala-azar dermal leishmaniasis (PKDL) collected from the present epidemic (1990s to date). They were seen to be similar to the two isolates of the 1970s epidemic. Interspecies differences were observed in different reference Leishmania species whereas no intraspecies difference was observed amongst the clinical isolates (8VL + 2PKDL) and all of these were found to be similar to L. donovani isolates of 1970s epidemic.

Animals↗
PubMed1994

Immunoblotting identifies an antigen recognized by anti gp63 in the immune complexes of Indian kala-azar patient sera.

In SDS-PAGE the immune complexes (IC) of kala-azar patient sera showed intense bands at 55 kDa and 20 kDa corresponding to heavy and light chains of immunoglobulins. In immunoblot experiment, kala-azar and normal IC after treatment with patient sera showed multiple bands of which the band at 55 kDa was most prominent in kala-azar IC. It is known that in kala-azar sera antihuman IgG is present, so the heavy band at 55 kDa region may be due to higher amount of IgG and/or other antigen(s) present at that region. Immunoblot experiments of kala-azar IC with anti gp63 also developed a major band at 55 kDa. It suggests that the antigen (55 kDa) and gp63 have common antigenic epitope (s). Normal IC did not react with anti gp63 indicating absence of this antigen in normal IC. Antigenic similarity between the IC antigen (55 kDa) and gp63 indicated that the former antigen may have been processed from gp63. In summary, identification of a parasite antigen (55 kDa) in IC of kala-azar patients sera may be useful in developing a serodiagnostic assay for visceral leishmaniasis.

Adolescent↗
PubMed1994

Chlorophyll and chlorophyllin as modifiers of genotoxic effects.

Reports on an inverse relationship between the consumption of fresh vegetables and human gastrointestinal cancer have been followed by screening for the protective activity of a large number of plant extracts, including leafy vegetables. Chlorophyll is ubiquitous in all green plant parts. Chlorophyllins are derivatives of chlorophyll in which the central magnesium atom is replaced by other metals, such as cobalt, copper or iron. An attempt has been made in this article to review the relative efficacy of chlorophyll and chlorophyllin in modifying the genotoxic effects of various known toxicants.

Animals↗
PubMed1994

Effect of denaturants and stabilisers on protein adsorption at solid-liquid interfaces.

The adsorption isotherms of different proteins from aqueous solution to the surface of different solids have been compared in the presence of additives such as urea, surfactants and high concentration of various neutral salts. The adsorption isotherms of lysozyme on alumina are not affected much in the presence of 8 M urea showing the rigid structure of lysozyme whereas isotherms of hemoglobin show surface coagulation even in presence of 2 M urea. In presence of 8 M urea, adsorption isotherms of BSA on alumina show two distinct steps. The extent of protein adsorption in the presence of surfactants depends on the nature of surfactants as well as of the underlying surface. The adsorption isotherms of BSA and lysozyme in presence of 2 M concentration of different neutral salts have also been compared with each other. In the presence of denaturants such as NaI and LiCl, the proteins are adsorbed in unfolded beta-conformation whereas in the presence of protein stabilizers such as NaCl, KCl and Na2SO4, amount of protein adsorbed at saturation is zero or extremely small showing that unfolding of proteins at the interface is necessary for initial stage of protein adsorption. The standard free energy change (delta G degrees) per square meter of the surface, signifying relative affinity of adsorption at the state of monolayer saturation, have been calculated. The magnitude of standard free energy of transfer (delta G degrees B) of one mole of protein to the surface in presence of all the additives was found close to 40 kJ/mole.

Absorption↗
PubMed1993

Differential protection of chlorophyllin against clastogenic effects of chromium and chlordane in mouse bone marrow in vivo.

The anticlastogenic activity of sodium-copper-chlorophyllin was tested against two known clastogens, chromium(VI) oxide and the pesticide chlordane, both of which occur as environmental toxicants. The chemicals were administered to male Swiss albino mice by gavage and chromosomes were studied from bone marrow cells 24 h after the exposure, following colchicine-air drying-Giemsa preparation. The end-points screened were the frequencies of chromosomal aberrations and damaged cells. The clastogenic effects induced by chromium in aqueous solution (20 mg/kg body weight) were reduced to a significant level by chlorophyllin (1.5 mg/kg body weight), when administered both before and simultaneously with the toxicant. The effects of chlordane in olive oil (10 mg/kg body weight) were, however, not reduced by the administration of chlorophyllin (1.5 and 3 mg/kg body weight).

Analysis of Variance↗
PubMed1993

Chronic hypothermia and water intoxication associated with a neurodegenerative disease.

We describe a 71 year old man with a neurodegenerative condition who developed chronic inappropriate antidiuretic hormone secretion and hypothermia resulting in recurrent episodes of impaired consciousness. This combination of abnormalities is attributable to hypothalamic disease and has not to our knowledge been previously reported with clearly documented antidiuretic hormone excess.

Aged↗
PubMed1993

Frusemide-induced diabetes mellitus in insulin pretreated rabbits as an experimental model.

Single dose of frusemide 0.1 mg/kg orally was administered in 10 rabbits pretreated with soluble insulin 4 IU intravenously. Induction of diabetes after 24 h was confirmed by an increase in blood sugar and glucosylated haemoglobin and a decrease in serum insulin levels. Ten diabetic rabbits which received only frusemide without insulin pretreatment were used as controls, whereas equal number of insulin-pretreated rabbits receiving hydrochlorothiazide 250 mg/kg orally served as the positive control group. All biochemical parameters remained unaltered in the frusemide-treated test group as well as the positive control group after two weeks. The pancreatotoxic effect of frusemide may induce a stable hyperglycaemic state in rabbits which could lead to a useful diabetic model.

Administration, Oral↗
PubMed1992

Isolation and characterization of a cyclic nucleotide-independent protein kinase from Leishmania donovani.

We describe here a protein kinase from the promastigote form of the parasitic protozoan, Leishmania donovani, purified to near homogeneity to a single-subunit, 34-kDa protein. This enzyme does not require a cofactor, and has several characteristics in common with the catalytic subunit of mammalian cAMP-dependent protein kinase, for example, preference for kemptide as a substrate, phosphorylation of serine residues of protamine and inhibition by the mammalian heat-stable inhibitor. The leishmanial enzyme can associate with the regulatory subunit of mammalian cAMP-dependent protein kinase to form an inactive holoenzyme that is activated by cAMP and is protected from inhibition by thiol reagents. From these results it is concluded that L. donovani promastigotes possess a protein kinase which has similar characteristics with the mammalian catalytic subunit of cAMP-dependent protein kinase.

Animals↗
PubMed1992

Absolute reaction rate and kinetics of protein adsorption at solid-liquid interfaces.

Extents of adsorption of bovine serum albumin from aqueous solution to the surface of alumina, silica, carbon and chromium powder have been studied as function of time for various values of bulk protein concentration, pH, ionic strength and temperature. The rates of adsorption in all cases have been observed to fit in the first order rate equation with two different rate constants Ka1 and Ka2. Effects of addition of SDS, CTAB and neutral salts on values of Ka1 and Ka2 have also been studied. Using Arrhenius equation the activation energy values Ea1 and Ea2 have been evaluated from the values of Ka1 and Ka2 at three different temperatures, respectively. The corresponding values of enthalpy of activation (delta H*), entropy of activation (delta S*), and free energy of activation (delta G*) have been evaluated using Eyring's equation of absolute reaction rate. The mechanism of protein adsorption has been discussed in the light of basic principles of absolute reaction rate. It has been found that for Ka1 the delta H*1 greater than T delta S*1 and for Ka2 T delta S*2 greater than H*2, i.e. the anchorage and binding of protein to the surface are enthalpy controlled processes whereas the surface denaturation as well as rearrangement and folding is an entropy controlled process. The role of diffusion on rate of adsorption has also been discussed.

Adsorption↗
PubMed1991

Biochemical and immunological characterization of exometabolites from an Indian strain of Leishmania donovani promastigotes grown in a chemically defined medium.

Exometabolites (EXOM) of an Indian strain of Leishmania donovani promastigotes isolated from a chemically defined medium by ultrafiltration consisted of proteins, glycoproteins, lipid and lipophosphopolysaccharide (LPPS). LPPS of Mr 40-28 kDa in SDS-PAGE could be labelled metabolically with [32P]-phosphate and recovered in the aqueous phase of hot-phenol-water extraction of EXOM (PE-Aq) along with a glycoprotein of Mr 150-130 kDa (GP150-130). These two molecules could be eluted from DE-52 column with 200 mM NaCl (D2). The 300 mM NaCl (D3) and 400 mM NaCl (D4) eluates from DE-52 column contained one unsaturated polar lipid component. The LPPS had Rf value of 0.65-0.75 in Thin Layer Chromatography (TLC) using saturated phenol water solvent system. EXOM revealed 15 bands in SDS-PAGE of which proteins of Mr 84, 66, 56, 50 and 29 kDa were prominent. When EXOM were fractionated through Con A-Sepharose column, the fraction eluted with alpha-methyl-D-mannoside (Con A-E) had seven bands as revealed by SDS-PAGE of which 25, 16, 13 and 12 kDa glycoproteins were prominent. The antigens present in EXOM can be classified as slower anodic migrating and faster anodic migrating antigens as revealed by immunoelectrophoresis (IEP). The slower anodic migrating antigens, LPPS and GP150-130 recovered in PE-Aq and D2 did not cross-react with kala-azar patients' sera but cross-reacted with homologous anti-promastigote sera. Two faster anodic migrating antigens which could be recovered in organic phase of hot phenol extraction of EXOM (PE-O) and eluted in D3 and D4 and Con A-E, cross-reacted with kala-azar patients' sera. The antigens of both the classes were sensitive to periodic acid oxidation.

Animals↗
PubMed1991

Aminoacetone synthase from goat liver. Involvement of arginine residue at the active site and on the stability of the enzyme.

The arginine-specific reagents phenylglyoxal and butane-2,3-dione inactivated goat liver aminoacetone synthase with pseudo-first-order kinetics, with the rate dependent on modifier concentration. Phenylglyoxal and butane-2,3-dione appeared to react with one arginine residue per enzyme molecule. The inactivated enzyme could be re-activated by Tris, suggesting additional evidence of modification of the arginine residue. Acetyl-CoA, one of the substrates, completely protected the enzyme from inactivation. Glycine gave partial protection. Protection by substrates against inactivation by phenylglyoxal and butane-2,3-dione suggested the presence of an essential arginine residue at the substrate-binding region. Experiments with [7-14C]phenylglyoxal in the presence of acetyl-CoA showed that only the arginine residue at the active site could be modified by phenylglyoxal. The stability of the enzyme is dependent on the presence of both EDTA and Mg2+.

Acetyl Coenzyme A↗
PubMed1991

Role of Ca2+ ion on Leishmania-macrophage attachment.

Leishmania donovani, the etiological agent for the disease visceral leishmaniasis, attach themselves to the macrophages for initiation of the disease. The attachment process has been found to be regulated by Ca2+ ions. Verapamil, a Ca(2+)-channel blocker inhibits Leishmania-macrophage attachment. The inhibitory effect is increased with time. Nifedipine, another Ca(2+)-channel blocker exhibits the same effect. The attachment process is stimulated by Ca(2+)-ionophore alone. The inhibitory effects of the calcium channel blockers are reversed by the ionophore.

Animals↗
PubMed1991

Identification of immune complex antigens in sera of Indian kala-azar patients.

Level of circulating immune complex (IC) in visceral leishmaniasis is much higher than that in control sera. In immunoblot experiment, treatment of kala-azar IC with patient sera showed at least 6 bands of which the band around 55 kDa region was most prominent. The band at 55 kDa is primarily due to the presence of an antigen recognized by its corresponding antibody present in the patient sera. This was confirmed by using radiolabelled antibody from kala-azar patient serum and antipromastigote serum. The heavy chain of IgG originating from IC is also present in the same region which was detected by its recognition with antihuman IgG. The IC gave a band at 55 kDa region with sea-urchin antitubulin. Kala-azar sera also reacted with purified rat brain tubulin. The present results suggest that a tubulin like protein is present at 55 kDa region along with the heavy chain of IgG.

Antigen-Antibody Complex↗
PubMed1990

Partial purification and characterization of a soluble protein kinase from Leishmania donovani promastigotes.

A soluble protein kinase from the promastigote form of the parasitic protozoon Leishmania donovani was partially purified using DEAE-cellulose, Sephadex G-200 and phosphocellulose columns. The enzyme preferentially utilized protamine as exogenous phosphate acceptor. The native molecular mass of the enzyme was about 85 kDa. Mg2+ ions were essential for enzyme activity; other metal ions, e.g. Ca2+, Co2+, Zn2+ and Mn2+, could not substitute for Mg2+. cAMP, cGMP, Ca2+/calmodulin and Ca2+/phospholipid did not stimulate enzyme activity. The pH optimum of the enzyme was 7.0-7.5, and the temperature optimum 37 degrees C. The apparent Km for ATP was 60 microM. Phosphoamino acid analysis revealed that the protein kinase transferred the gamma-phosphate of ATP to serine residues in protamine. The thiol reagents p-hydroxymercuribenzoic acid, 5-5'-dithio-bis(2-nitrobenzoic acid) and N-ethylmaleimide inhibited enzyme activity; the inhibition by p-hydroxymercuribenzoic acid and 5-5'-dithio-bis(2-nitrobenzoic acid) was reversed by dithiothreitol.

Adenosine Triphosphate↗
PubMed1989

Electrical conduction in some nucleic acid base complexes with acridine orange dye: study of localized levels.

Semiconduction activation energies of adenine, guanine, thymine and uracil complexes with acridine orange dye at various dye concentrations were measured in both Ohmic and space charge limited (SCL) current regimes. The behaviour of the complexes is non-extrinsic at high dye concentrations but extrinsic at low dye concentrations. Dominant electron and hole levels are shown to depend also on dye concentration. Various transport parameters have been evaluated.

Acridine Orange↗
PubMed1989

Evaluation of antileishmanial activity of trans-aconitic acid.

TAA, an inhibitor of the enzyme aconitase, inhibits the growth of L. donovani promastigotes. Morphogenic transformation of the amastigote to the promastigote (table; see text) form in vitro was also inhibited by 2 mM TAA. TAA also reduced multiplication of the parasite in macrophage culture. In the hamster model of leishmania, TAA significantly reduced the parasitic burden of liver. In acute toxicity tests with BALB/c mice no deaths were recorded even at a dose level of 2 g/kg body wt/day.

Aconitic Acid↗