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Biomedical subjects

J Mitra

Publications and source records attributed to J Mitra.

At least 19 recordsLinked to original sources
PubMed2001

Bioremediation of DDT in soil by genetically improved strains of soil fungus Fusarium solani.

Bioremediation of DDT in soil by genetically improved recombinants of the soil fungus Fusarium solani was studied. The parent strains were isolated from soil enriched with DDD or DDE (immediate anaerobic and aerobic degradation products of DDT), as further degradation of these products are slow processes compared to the parent compound. These naturally occurring strains isolated from soil, however, are poor degraders of DDT and differed in their capability to degrade its metabolites such as DDD, DDE, DDOH and DBP and other organochlorine pesticides viz. kelthane and lindane. Synergistic effect was shown by some of these strains, when grown together in the medium containing DDD and kelthane under mixed culture condition. No synergism in DDE degradation was observed with the strains isolated from enriched soil. DDD-induced proteins extracted from individual culture filtrate (exo-enzyme) when subjected to SDS-Polyacrylamide Gel Electrophoresis (SDS-PAGE) showed complementary polypeptide bands in these strains i.e., each strain produced distinct DDD degrading polypeptide bands and the recombinant or hybrid strains produced all of the bands of the two parents and degraded DDD better than the parental strains. Recombinant hybrid strains with improved dehalogenase activity were raised by parasexual hybridisation of two such complementary isolates viz. isolate 1(P-1) and 4(P-2) showing highest complementation and are compatible for hyphal fusion inducing heterokaryosis. These strains are genetically characterised as Kel+Ben(R)DBP-Lin- and Kel-Ben(r)DBP+Lin+ respectively. Recombinants with mixed genotype, i.e., Kel+Ben(R)DBP+Lin+ showing superior degradation quality for DDT were selected for bioremediation study. Recombination was confirmed by polypeptide band analysis of DDD induced exo-proteins from culture filtrate using SDS-Polyacrylamide Gel Electrophoresis (PAGE) and RAPD (Random Amplified Polymorphic DNA) of genomic DNA using PCR (Polymerase Chain Reaction) technique. SDS-PAGE showed combination of DDD induced polypeptide bands characteristic of both the parents in the recombinants or the hybrids. PCR study showed the parent specific bands in the recombinant strains confirming gene transformation.

Biodegradation, Environmental↗
PubMed2001

S and G2 phase roles for Cdk2 revealed by inducible expression of a dominant-negative mutant in human cells.

Cyclin-dependent kinase 2 (Cdk2) is essential for initiation of DNA synthesis in higher eukaryotes. Biochemical studies in Xenopus egg extracts and microinjection studies in human cells have suggested an additional function for Cdk2 in activation of Cdk1 and entry into mitosis. To further examine the role of Cdk2 in human cells, we generated stable clones with inducible expression of wild-type and dominant-negative forms of the enzyme (Cdk2-wt and Cdk2-dn, respectively). Both exogenous proteins associated efficiently with endogenous cyclins. Cdk2-wt had no apparent effect on the cell division cycle, whereas Cdk2-dn inhibited progression through several distinct stages. Cdk2-dn induction could arrest cells at the G1/S transition, as previously observed in transient expression studies. However, under normal culture conditions, Cdk2-dn induction primarily arrested cells with S and G2/M DNA contents. Several observations suggested that the latter cells were in G2 phase, prior to the onset of mitosis: these cells contained uncondensed chromosomes, low levels of cyclin B-associated kinase activity, and high levels of tyrosine-phosphorylated Cdk1. Furthermore, Cdk2-dn did not delay progression through mitosis upon release of cells from a nocodazole block. Although the G2 arrest imposed by Cdk2-dn was similar to that imposed by the DNA damage checkpoint, the former was distinguished by its resistance to caffeine. These findings provide evidence for essential functions of Cdk2 during S and G2 phases of the mammalian cell cycle.

Base Sequence↗
PubMed1999

Induction of p21(WAF1/CIP1) and inhibition of Cdk2 mediated by the tumor suppressor p16(INK4a).

The tumor suppressor p16(INK4a) inhibits cyclin-dependent kinases 4 and 6. This activates the retinoblastoma protein (pRB) and, through incompletely understood events, arrests the cell division cycle. To permit biochemical analysis of the arrest, we generated U2-OS osteogenic sarcoma cell clones in which p16 transcription could be induced. In these clones, binding of p16 to cdk4 and cdk6 abrogated binding of cyclin D1, p27(KIP1), and p21(WAF1/CIP1). Concomitantly, the total cellular level of p21 increased severalfold via a posttranscriptional mechanism. Most cyclin E-cdk2 complexes associated with p21 and became inactive, expression of cyclin A was curtailed, and DNA synthesis was strongly inhibited. Induction of p21 alone, in a sibling clone, to the level observed during p16 induction substantially reproduced these effects. Overexpression of either cyclin E or A prevented p16 from mediating arrest. We then extended these studies to HCT 116 colorectal carcinoma cells and a p21-null clone derived by homologous recombination. In the parental cells, p16 expression also augmented total cellular and cdk2-bound p21. Moreover, p16 strongly inhibited DNA synthesis in the parental cells but not in the p21-null derivative. These findings indicate that p21-mediated inhibition of cdk2 contributes to the cell cycle arrest imposed by p16 and is a potential point of cooperation between the p16/pRB and p14(ARF)/p53 tumor suppressor pathways.

Apoptosis↗
PubMed1999

The geographical data of the Kāśyapa Samhitā.

One of the parameters in ascertaining the date of the Kashyapa Samhita is the data of geography referred to there in. Geography abounds various spheres like country, province, city, river, mountain and sea. The whole geographical material is mentioned in the chapter "Bhojana Kalpa" of the Kalpasthana, 22nd and 25th chapters of the Khilasthana.

Geography↗
PubMed1998

Temperature-induced conformational changes in prosomatostatin-II: implications for processing.

Somatostatin (SRIF) is a 14-residue peptide hormone synthesized in the hypothalamus and pancreatic islets. SRIF-14 and an N-terminally extended form, SRIF-28, are generated by the proteolytic processing of an approx. 102-residue precursor prosomatostatin (proSRIF) at a single set of paired basic residues (Arg-Lys) and at a monobasic (Arg) site respectively. Previous work in our laboratory demonstrated that the propeptide of SRIF mediates intracellular sorting; we suggested that this information resides in the prohormone structure. To identify putative sorting domains we have investigated structural features of recombinant anglerfish proSRIF-II purified from Escherichia coli. Two species of proSRIF-II were obtained: a monomeric form and a disulphide-linked dimer. CD analyses revealed that monomeric proSRIF-II lacks appreciable periodic secondary structure; however, on slow heating (2 degrees C/min) and cooling, it assumed a predominantly alpha-helical conformation. When subjected to a second heating-and-cooling cycle, the alpha-helical conformation was maintained. In contrast, the dimeric form of proSRIF-II was predominantly alpha-helical and its helicity did not increase in response to heating and recooling. Our results suggest that proSRIF-II might exist in several different folding intermediate states.

Amino Acid Sequence↗
PubMed1996

Regulation of the acquisition of meiotic competence in the mouse: changes in the subcellular localization of cdc2, cyclin B1, cdc25C and wee1, and in the concentration of these proteins and their transcripts.

During their development, mammalian oocytes acquire the ability to resume meiosis. We demonstrate that the concentration of p34cdc2 increases during the acquisition of meiotic competence, as determined by immunoblotting, whereas the concentration of cyclin B1 decreases. Laser-scanning confocal microscopy corroborated these changes and furthermore indicate that an increase occurs in the nuclear concentration of each protein. Results of immunoblotting experiments demonstrate that associated with the acquisition of meiotic competence is an increase in the concentration of cdc25C, an activator of p34cdc2/cyclin B kinase, and a decrease in wee1, an inhibitor of cdc2/cyclin B kinase. These changes were again corroborated by laser-scanning confocal microscopy, which also indicates that an increase in the nuclear concentration of wee1 occurs. The concentration of the transcripts encoding these proteins, however, is essentially similar in meiotically incompetent and competent oocytes. Thus, these changes in protein concentration that occur during oocyte development likely reflect changes in the translational efficiency of their mRNAs. Consistent with this is that the relative rate of synthesis of p34cdc2 in meiotically competent oocytes is approximately 3 times greater than that in meiotically incompetent oocytes, whereas the stability of newly synthesized p34cdc2 is essentially the same in each cell type.

Animals↗
PubMed1995

Glimpses of the advancement of medical science as depicted in the Mahäbhärata.

The Mahabharata of Vedavyasa is an encyclopaedic work, which has got some importance from the standpoint of Indian medical science also. According to it Ayurveda was a compulsory subject which was taught to everybody. Perhaps, Mahabharata is the first epic which presents the term Ayurveda. The fundamentals of Ayurveda are discussed in it very well. Circulations of blood described here reminds us the same of sushruta samhita. Three types of poisons and a number of metals and jewels have also been given in Mahabharata.

History, Ancient↗
PubMed1994

Ca2+ dependent activation of rat uterine glycerylphosphorylcholine diesterase: presence of a positive modulator protein in uterine secretion.

The rat uterine secretory enzyme glycerylphosphorylcholine (GPC) diesterase (EC 3.1.4.2) had been purified and characterized previously with respect to its mol. wt., size, amino acid, carbohydrate composition and estrogen inducible properties. This enzyme is observed to have exclusive specificity for GPC and exhibits characteristic hyperbolic kinetics with Ca2+ in an ethyleneglycolbis N'N'N'N' tetraacetic acid (EGTA) buffered system. Ca2+ reduces Km of the enzyme for GPC from 0.65 to 0.25 mM. The Km for GPC of the partially purified enzyme is found to be 0.35 mM without addition of calcium which indicates the presence of a positive modulator of the enzyme in this fraction. Based on this rationale, a protein activating factor for the enzyme was isolated from this fraction which has a native size of 18 KD as observed on Sephacryl S-200 chromatography and strikingly stimulates enzyme activity at around 0.55 microM.

Animals↗
PubMed1994

Association of glycerylphosphorylcholine with human sperm and effect of capacitation on their metabolism.

The presence and localization of glycerylphosphorylcholine (GPC) on the surface of human sperm, as well as the metabolism of its breakdown product L-glycerol 3 phosphate (G3P), were investigated. GPC was found to be associated with sperm after penetrating cervical mucus and was present after repeated washing of the sperm. GPC was partially released by treatment with 0.4 M NaCl in 0.01 M sodium phosphate buffer (pH 7.4) and localized to the head region after sperm fractionation. G3P did not increase O2 uptake of uncapacitated human sperm. However, under aerobic conditions, lactate accumulated when exogenous G3P or uterine GPC diesterase was added to sperm in suspension. The uptake of O2 by washed capacitated sperm pre-incubated with 1 unit of rat uterine GPC diesterase for 30 min was significant. This effect was inhibited by 2 microM oligomycin indicating that oxidative phosphorylation had occurred. The present study indicates that GPC may play a role in the metabolism of human sperm after capacitation.

Glycerophosphates↗
PubMed1993

Intramedullary sodium cyanide injection on respiratory and vasomotor responses in cats.

To examine the effect of hypoxia confined to the ventrolateral medulla we microinjected NaCN into the cat medulla (1.0 mm below the ventral surface) unilaterally and investigated cardio-respiratory changes. We studied anesthetized artificially ventilated animals and measured the electrical activity of phrenic and cervical sympathetic nerves and blood pressure. Histotoxic hypoxia depressed phrenic amplitude and elevated sympathetic tone and blood pressure. These responses were obtained predominantly from the region 5.0-8.0 mm caudal to the foramen caecum and 3.0-5.0 mm lateral to the midline (intermediate area). A study with 14C-cyanide showed that total and covalently bound cyanide was confined within a 1 mm diffusion sphere following microinjection. Isolated areas in both rostral and caudal medulla responded to cyanide with elevated sympathetic tone in the absence of phrenic nerve depression, suggesting dissociation of respiratory and vasomotor responses to hypoxia. Thus, the respiratory depression and vasomotor excitation produced by central hypoxia can be reproduced by hypoxia limited to discrete regions of the ventrolateral medulla.

Animals↗
PubMed1992

Cardiorespiratory changes induced by vertebral artery injection of sodium cyanide in cats.

Brain stem hypoxia caused by vertebral artery injection of sodium cyanide (NaCN) (1-20 micrograms) in artificially ventilated cats depressed phrenic and stimulated sympathetic nerve activity with a simultaneous increase in arterial blood pressure. Larger doses of NaCN caused greater effects. Hypercapnia produced by inhalation of 7% CO2 in O2 tended to reduce NaCN-induced responses on phrenic activity but not on blood pressure or sympathetic activity. Infusion into the vertebral artery with hypoxic saline (3% CO2 in N2) altered blood pressure, also affecting phrenic and sympathetic nerves similarly to NaCN administration. However, washout of CO2 by infusion of 100% O2 bubbled saline at high flow rates (3.6 ml/min) depressed phrenic as well as sympathetic activity and blood pressure. Spinal transection at the first cervical level eliminated sympathetic excitatory response to intravertebral cyanide injection. However, a large dose of NaCN (600 micrograms) given intravenously in spinal animal excited sympathetic activity. We conclude that intravertebral injection of NaCN can be used to study the effects of local hypoxia of the brain stem on cardiorespiratory responses and that hypoxia acts at both these sites (brain stem and spinal cord) to stimulate sympathetic excitation.

Animals↗
PubMed1992

Detection of canine homologs of human MYC, BCL2, IGH, and TCRB genes by Southern blot analysis.

Subsets of non-Hodgkin's lymphoma in humans have been shown to involve activation of protooncogenes such as MYC and BCL2 resulting from chromosome translocation involving the IGH and TCR genes. Malignant lymphomas in the canine present histologic and clinical subsets similar to those in humans. To study the genetic nature of these lymphomas, we undertook this study to determine, by Southern blotting analysis, the extent of homology between the human and canine genes MYC, BCL2, IGH, and TCRB using human gene probes. Our results, presented here, show that the organization of these genes in the two species is very similar.

Animals↗
PubMed1992

Glycerylphosphorylcholine (GPC) diesterase related alterations in the oxygen consumption profile of rat spermatozoa in differing functional states.

The functional interaction of the estrogen-induced uterine enzyme glycerylphosphorylcholine (GPC) diesterase with epididymal rat sperm before and after incubation under capacitating conditions was investigated indirectly, by measuring the glycerol phosphate (GP) released on enzymatic hydrolysis of GPC and using oxygen consumption as a measure of oxidative phosphorylation by the sperm. Freshly released, washed sperm metabolized GP but not GPC. Utilization of GP was found to be inhibited by 2 microM oligomycin but was enhanced dose-dependently in the presence of the uncoupling agent, 2,4-dinitrophenol, indicating that the process was essentially similar to that occurring in somatic mitochondria in that it involved electron transport via ubiquinone and the cytochrome system and was coupled to ATP synthesis. However, on incubation of sperm under conditions supporting capacitation, which led to a striking increase in oxygen consumption, the presence of GP decreased oxygen uptake significantly, in a manner similar to that occurring in the presence of the glycolysable substrate, glucose. The implications of these GPC diesterase-induced metabolic alterations in sperm function are discussed.

Animals↗
PubMed1992

Nonvagal modulation of hypoglossal neural activity.

Upper airway dilating muscle activity is characterized by an early-peaking pattern which serves to dilate or stiffen the upper airway at the time when the greatest negative intraluminal pressure is generated by contraction of chest wall muscles. This pattern has been attributed to phasic afferent inputs from pulmonary stretch receptors. The present study examines the hypothesis that nonvagal factors may also influence the discharge pattern and coordination of upper airway and chest wall muscle activities. Therefore, in anesthetized, paralyzed, vagotomized and artificially ventilated cats, we examined the effects of changes in respiratory drive produced by activation of cholinergic and GA-BAergic (gamma-aminobutyric acid) receptors at the ventrolateral aspects of the medulla oblongata on phasic intrabreath discharge patterns of hypoglossal and phrenic nerves. Cholinergic agents (acetylcholine, carbachol, methacholine, physostigmine) applied directly to chemoreceptive areas on the ventral medullary surface increased hypoglossal activity, and in addition converted inspiratory discharge from an augmenting to a decrementing pattern of activity. The reverse effect on the discharge pattern of hypoglossal activity was observed with a decrease in respiratory drive. While the amplitude of the phrenic nerve discharge was also affected by these interventions, the augmenting discharge pattern of phrenic nerve activity did not change. These results suggest that the early peaking pattern of hypoglossal nerve discharge in vagotomized cats also depends on the level of respiratory drive, and is not solely dependent on vagal afferent inputs. In addition, the data suggest that structures near the ventral surface of the medulla are influential in shaping the pattern of hypoglossal nerve activity and maintaining balanced activity of upper airway and chest wall muscles.

Acetylcholine↗
PubMed1991

Alteration of phrenic high frequency oscillation by local cooling of the ventral medullary surface.

Cooling of small sites on the ventral medullary surface of the cat produces a decrease in frequency of phrenic high frequency oscillation (HFO). The effect on HFO frequency of cooling near the hypoglossal rootlets, but not the effect of cooling near the inferior cerebellar artery, can be completely offset by raising arterial pCO2 to restore phrenic activity to its precooling level. Thus, structures near the ventral medullary surface are important for generation or propagation of phrenic HFO. The effect of cooling of the 'intermediate area' cannot be entirely explained as depression of putative central chemoreceptor activity.

Animals↗
PubMed1991

Effect of DDT on plant mineral nutrition.

DDT added to soil at a concentration of 50 microg g(-1) had no inhibitory effects on germination and plant growth of barley, mung and rice, but considerably inhibited the oilseed species tested in the laboratory. The uptake of one or other ions was affected in varying degrees, with plants grown in DDT-treated soils. Detailed field studies of a peanut crop further confirmed the inhibition of ion uptake with DDT, especially Ca(2+) and K(+). Reduced uptake of (86)Rb by germinated peanut seeds in the presence of DDT further supported the observations made with K(+). Cell number and length in plants were reduced in plants grown in DDT-treated soil and the role of calcium is discussed. It appears that growth inhibition in oil seed plants may arise from the low levels of Ca(2+) and K(+) in plants grown in DDT-treated soils.

Journal Article↗