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1.
Extracellular signals are transduced across the cell by the cell surface receptors, with the aid of G-proteins, which act
at a critical point of signal transduction and cellular regulation. Structurally, G-proteins are heterotrimeric consisting
α, β and γ subunits but in functionally active state they dissociate into α subunit coupled to GTP and as βγ dimer. G-proteins
can be broadly divided into two classes based on their sensitivity to pertussis toxin and cholera toxin. Existence of various
forms of each of the subunit allows molecular diversity in the subunit species of G-proteins. These subunits interact with
a wide range of receptors and effectors, facilitated by post translational modification of their subunits. Different types
of G-proteins mediate several signalling events in different parts of the body. This review summarizes the features of (i)
structural and functional heterogenity among different subunits of G-proteins, (ii) interaction of G-proteins and their subunits
with effectors with specific cases of G-protein mediated signalling in olfaction, phototransduction in the retina,
ras andras
related transduction and (iii) disease conditions associated with malfunctioning of G-proteins. 相似文献
2.
Rajiv K. Saxena 《Journal of biosciences》1997,22(1):3-12
Some murine (YAC, P815 and SP20) and human (Molt4, Raji and HR7) tumour cell lines were (i) treated with IFN-γ for inducing
enhanced expression of MHC class I antigen, or (ii) given a brief treatment with citrate buffer (pH 3.0), which resulted in
denaturation of class I MHC antigens on these tumour cells. IFL-γ or acid treated tumour cells were used as unlabelled competing
targets in cold target inhibition assays. The results indicated that the competing ability of acid-treated tumour cells remained
unaltered, whereas IFN-γ treated tumour cells competed with significantly less efficiency. These results have been evaluated
in light of the current view of NK cell development and the expression of inhibitory receptors for MHC class I molecules (IRMs),
on NK cells. A modified view on NK cell heterogeneity based upon IRM expression has been proposed which reconciles several
apparently discordant observations about the activity and role of NK cells. Two classes of NK cells have been proposed. Type
I NK ceils have target recognition receptors which do not recognize autologous normal cells, lack IRMs, and may participate
in first line of defence against transformed cells
in vivo. Type II NK cells have target recognition receptors for autologous normal cells and express at least one self-reactive IRM
in order to prevent auto-killing. Type II NK cells participate in killing those transformed cells which down-regulate their
MHC class I expression in order to escape cytotoxic T-cell surveillance. It is also postulated that mechanism of inverse correlation
of target cell MHC class I expression levels and their susceptibility to NK cells, involves interference model of missing
self hypothesis for type I NK cells and inhibitory signal model of missing self hypothesis for type II NE cells. Finally,
it is proposed that acid treatment of tumour cells enhances their lysis susceptibility by making them additionally susceptible
to type II NK cells, rather than enhancing their killing by type I NK cells. This proposition would explain the lack of effect
of acid treatment on the competing ability of tumour cells, when target cells are only lysed by type I NE cells. 相似文献
3.
Amino acid sequences of proteinaceous proteinase inhibitors have been extensively analysed for deriving information regarding
the molecular evolution and functional relationship of these proteins. These sequences have been grouped into several well
defined families. It was found that the phylogeny constructed with the sequences corresponding to the exposed loop responsible
for inhibition has several branches that resemble those obtained from comparisons using the entire sequence. The major branches
of the unrooted tree corresponded to the families to which the inhibitors belonged. Further branching is related to the enzyme
specificity of the inhibitor. Examination of the active site loop sequences of trypsin inhibitors revealed that here are strong
preferences for specific amino acids at different positions of the loop. These preferences are inhibitor class specific. Inhibitors
active against more than one enzyme occur within a class and confirm to class specific sequence in their loops. Hence, only
a few positions in the loop seem to determine the specificity. The ability to inhibit the same enzyme by inhibitors that belong
to different classes appears to be a result of convergent evolution. 相似文献
4.
The tachykinins are a family of gastrointestinal peptides comprising eight members: substance P, neurokinin A, neurokinin
B, eledoisin, physalemin, uperolein, kassinin and phyllomedusin. Consensus dynamics was carried out on an
ensemble
of seven tachykinins to determine the binding conformation of the common C-terminal fragment: Phe-X-Gly-Leu-Met-NH
2
,the ’message sequence’ of tachykinins. Three binding modes for the C-terminal pentapeptide were determined. The first binding
conformation is folded due to an intramolecular H-bond between the NH of the variable residue (X) and CO of Met. Other features
include γ-bends at both the variable amino acid (X) and at Gly. The global minimum of the simulation has this conformation
for the C-terminal pentapeptide. The other two binding modes have slightly higher energies. The second is chiefly characterized
by a β-turn around the segment X-Gly-Leu-Met, with additional β-bends at the variable amino acid (X) and Met. The final binding
conformation is composed of β-bends around the variable amino acid (X) and Leu, and a ’pseudo’ γ-bend at the terminal Met.
This paper was presented at the MBU Silver Jubilee Symposium on Structural Biology and 24th Annual Meeting of the Indian Biophysical
Society held at Indian Institute of Science, Bangalore, Dec. 9–12, 1996. 相似文献
5.
The ultradian rhythm of the lateral leaflets ofDesmodium motorium}(Houtt.) Merril. was recorded with a picture analysis method using a video camera and a computer. The periods are in the minute
range and depend strongly on temperature.
The phosphatidyl inositol signal chain might be involved in the ultradian rhythm of the lateral leaflet movement of
Desmodium motorium:Myoinositol shortens the period length and reduces the known period lengthening effect of lithium ions. Neomycin, which inhibits
the hydrolysis of phosphatidylinositol-4,5 -biphosphate to inositol-4-phosphate and diacylglycerin, lengthens the period of
the rhythm at low concentrations (0.2 mM). Higher concentrations shorten the period, perhaps by activating G protein. Mastoparan,
which activates G protein, shortens period likewise. The G protein agonists fluorid ion and ethanol are toxic for the lateral
leaflets and could therefore not be used to test the involvement of G protein.
The intracellular Ca
2+
antagonist 3,4,5-trinietlioxybeiizoic acid 8-(diethylamino)octylester lengthens the period of the rhythm. This indicates,
that release of Cas
2+
from intracellular stores is important for the lateral leaflet movement rhythm. 相似文献
6.
Twenty four shift workers (8 from a steel industry and 16 from a Government hospital) participated in the study. The subjects
were instructed to self-measure oral temperature, 4 6 times a day for about three weeks. Sleep quantity and quality for each
subject were analysed with the help of an appropriate inventory. The data were analysed by cosinor and power spectrum methods.
The frequency of circadian rhythm detection was in the order of 48% in senior nurses, 29% in steel plant workers and 14% in
junior nurses. These were also complemented by the results of power spectrum analysis. Present results suggest that rhythms
of subjective fatigue and subjective drowsiness are governed neither by oral temperature oscillator nor by the sleep/wake
cycle oscillator. The results show that shift rotation pattern chiefly modulates the circadian time structure of shift workers.
It is also suggested that the phenomenon of circadian rhythm desynchronization in oral temperature appears to be independent
of per day total sleep length. 相似文献
7.
Two yolk proteins (YP1 and YP2) from the ovaries of Indian major carp, Labeo rohita were isolated by gel filtration and partially
characterized by the use of hydroxyapatite ultrogel column in conjunction with native PAGE. On native PAGE YP1 gave a single
protein band, whereas YP2 of gel filtration revealed the contamination of YP1, which was removed by adsorption chromatography
on hydroxyapatite ultrogel and then the YP2 was the purified one as judged by electrophoresis. Both YP1 and YP2 also stained
for lipid and contained alkalilabile phosphorus. Therefore, both yolk proteins were lipophosphoprotein. The molecular weights
of YP1 and YP2 were 620 kDa and 225 kDa respectively as determined by gel filtration on Sepharose 4B. When YP1 and YP2 were
compared in relation to some physicochemical characteristics with yolk proteins of other oviparous vertebrates including fish,
they were lipovitellin like.
Antiserum to YP2 crossreacted with YP2 and vitellogenin suggesting that YP2 was the cleaved product of vitellogenin. Anti-YP2
antiserum was not crossreacted with native YP1, whereas reduced and/or denatured YP1 was crossreacted indicating the presence
of antigenic determinants in the inner core region of YP1 polypeptide. 相似文献
8.
This paper presents the results of an investigation on the distribution of210Po in Mutharasanallur pond ecosystem. It has been demonstrated that210Po is non-uniformly distributed within the ecosystem. The results of the study show a dissolved210Po concentration in pond water of 1 4mBq 1−1. The sediment samplso recorded a210Po activity of 59 9 Bq kg−1. The aquatic organisms showed differential accumulation of the radionuclide with enhanced bioaccumulation in soft tissues
and muscle. The210Po activity in the biota fell within the range of 1·2–53 3 Bq kg−1 (wet wt). The bivalve mussel,Lamellidens marginalis was identified to accumulate higher concentration of210Poin soft tissues, suggesting that these organisms could serve as a bio-monitor of210Po radionuclide in a freshwater system. The concentration factors of210Po for the biotic components ranged from ∼102–∼104. Analyses of the results indicate that prawn and fish represent an important source of supply of210Po to humans via dietary intake. Results of210Po activity in the abiotic and biotic components of the pond ecosystem were higher when compared with those of Cauvery river
system, the primary water source of the pond. 相似文献
9.
Surender S. Katoch 《Journal of biosciences》1997,22(3):299-314
Endothelin-1, a potent vasoconstrictor peptide produces concentration dependent contractions in lamb tracheal smooth muscle.
These contractions are not inhibited by low doses (up to 20 μM) of trifluoroperazine and W-7, the calmodulin/myosin light
chain kinase (MLCK) inhibitors. At higher concentrations (200 μM), a delayed and poor reversal of isometric tensions results.
These relaxations are coupled with a partial dephosphorylation of regulatory myosin light chain (MLC). Preincubation of fiber
strips in MLCK inhibitors (200 μM) results in a delayed and attenuated contractile response but without a dephosphorylation
of MLC. H-7, a putative protein kinase C antagonist (25–100 μM) abolishes endothelin-1 induced contractile effects rapidly
(50% relaxation within 1–3 min). Moreover, such relaxations are accompanied by complete dephosphorylation of MLC. Phorbol
12, 13-dibutyrate, an exogenous activator of protein kinase C potentiates the endothelin induced contractions. Inactive phorbol
ester, 4α-phorbol ester does not elicit any contractile response in the muscle. The down regulation of protein kinase C, on
the other hand suppresses such potentiated contractile responses. These results suggest that endothelin-1 induced contractile
tensions in tracheal smooth muscle are mediated by a mechanism that involves an activation of enzyme protein kinase C. 相似文献
10.
Gábor Nardai Tamás Schnaider Csaba Söti Michael T. Ryan Peter B. Hoj János Somogyi Peter Csermely 《Journal of biosciences》1996,21(2):179-190
The 90 kDa heat shock protein (HSP90) is an ATP-binding molecular chaperone with an associated ATPase activity having nucleoplasmin
and HSP70-binding homology domains and containing Ca-binding EF-hands and a nuclear localization signal. Here we characterize
the HSP90-associated ATPase and show that it is (i) a P-type ATPase inhibited by molybdate and vanadate, (ii) able to hydrolyze
methylfluorescein phosphate with a 5–6-fold higher affinity, (iii) a 3-times better GTPase than ATPase in the presence of
calcium and (iv) HSP27 and F-actin, but not HSP10 can “convert” the HSP90-associated ATPase activity to HSP90 autokinase activity.
The HSP90-associated ATP/GTPase may participate in the regulation of complex formation of HSP90 with other proteins, such
as F-actin, tubulin and heat shock proteins. 相似文献
11.
Development of the second and third order auditory nuclei—nucleus magnoscellularis (NM) and nucleus laminaris (NL) respectively—was
studied using Nissl stained serial sections from brain specimens between 8 day of incubation and posthatch day 1, at every
two day interval. Reconstruction of these nuclei from three incubation ages showed progressive growth of both nuclei in a
rostrocaudal direction. The volume, total neuron, dead cell and glial cell numbers were estimated using stereological quantitation
methods. Both nuclei, while undergoing an overall gradual increase in volume up to 20 days registered a transient drop in
volume; earlier for NM at 10 days and later for NL at 18 days. From day 20 the two nuclei showed accelerated growth in volume.
The total neuron count rapidly declined up to 12 days with 43% loss of neurons in NM followed by a rise and later stabilization
within a certain range. The NL, however, showed a continuous fall in neuron numbers throughout the incubation period with
20% cell loss by day 12 and an overall loss of 52%. Cell death in both nuclei was maximal at 16 days and spanned the entire
period of incubation. Glia showed a biphasic increase with peak at 14 days for both NM and NL followed by a subsequent rise
at day 20 for both nuclei. These data would help in planning further experimental studies of auditory manipulation. 相似文献
12.
13.
Energy and economic efficiencies were evaluated on young (6 year) and old (20 year) jhum fields in Mizoram, north-eastern
India during second year of cropping, and were compared with those in the first year. The effect of auxiliary measures such
as tilling the soil or application of fertilizers (chemical or farm-yard manure or both in combination) was also examined
on energy and economic efficiencies. The results indicated that traditional jhum cultivation is labour intensive and energy
efficient, producing almost 15–20 times of energy invested. Energy and economic efficiencies decline with shortening of jhum
cycle. These efficiencies decline further from first to second year of cropping. Tilling is not useful to improve either energy
or economic efficiency. Fertilizer application, which is though profitable from the point of view of economic efficiency,
is highly energy inefficient. Application of fertilizers during second year cropping can be encouraged. Organic manuring may
be a better option than others to alleviate energy efficiency. However, a combination of organic and inorgamic manuring could
be the best option to enhance economic efficiency. 相似文献
14.
A thermophilic fungus Thermomyces lanuginous strain IISc 91, secreted one form each of α-amylase and glucoamylase during growth.
Both enzymes were purified to homogeneity by ion-exchange and gel-filtration chromatography and obtained in mg quantities.
α-Amylase was considered to be a dimeric protein of ∼ 42 kDa and contained 5% (by mass) carbohydrate. It was maximally active
at pH 5.6 and at 65°C. It had an activation energy of 44 kJ mol-1. The apparent Km for soluble starch was 2.5 mg ml-1. The enzyme produced exceptionally high levels of maltose from raw potato starch. At 50°C, the enzyme was stable for > 7h.
At 65°C, α-amylase was nearly 8-times more stable in the presence of calcium. Addition of calcium increaed the melting temperature
of α-amylase from 66°C to 73°C. Upon incubation at 94°C, α-amylase was progressively and irreversibly inactivated, and converted
into an inactive 72 kDa trimeric species.
Glucoamylase was a monomeric glycoprotein of ∼ 45 kDa with a carbohydrate content of 11% (by mass). It effected up to 76%
conversion of starch in 24 h producing glucose as the sole product. Its apparent Km for soluble starch was 0.04 mg ml-1 and Vmax was 660 Mmol glucose min-1 mg protein-1. It also hydrolyzed maltose. Its activity on maltooligosaccharides increased with the chain length of the substrates. Glucoamylase
was stable at 60°C for over 7h. Its activation energy was 61 kJ mol-1 Glucoamylase did not show synergistic effect with α-amylase. The properties of α-amylase and glucoamylase of Thermomyces
lanuginosus strain IISc 91 suggest their usefulness in the commercial production of maltose and glucose syrups. 相似文献
15.
V. Chenthamarakshan K. Cheirmaraj M. V. R. Reddy B. C. Harinath 《Journal of biosciences》1997,22(1):91-98
Bancroftian filariasis is a major public health problem affecting about 120 million people all over the world. Immunoprophylaxis
may serve as an additional adjunct along with chemotherapy and anti larval measures for successful filaria control. Circulating
filarial antigen fraction (CFA2-6) containing 43 kDa antigen and adultBrugia malayi sodium dodecyl sulphate (S DS) soluble antigen fraction BmA-2 with a 120 kDa molecule were earlier shown to be reactive with
endemic normal sera by immunoblotting and indirect ELISA techniques. BmA-2 was found to be highly cross reactive with CFA2-6. Sera raised against both the antigen fractions showed about 90 % cytotoxicity to the parasites in the presence of jird
peritoneal cells inin vitro as well as byin situ micropore chamber implantation technique. Further inin vivo studies using animal model, jirds CFA2-6 and BmA-2 could induce about 90% protection to infection in immunized animals. In passive transfer studies of immunity
it has been observed that BmA-2 induced protection is mainly antibody mediated. 相似文献
16.
Human peripheral blood mononuclear cells (PBMCs) activated with Con-A release a soluble factor which augments the expression
of class I major histocompatibility complex (MHC) antigens by a variety of tumour cells. Previous attempts to purify this
factor called MHC-activating factor (AF) (MHC-AF) made us realize that the presence of large numbers and quantities of irrelevant
fetal calf serum proteins in the culture supernatants of the activated human PBMCs, interfered with the purification procedure.
It was therefore necessary to standardize the use of a serum free culture medium to generate human MHC-AF. In the present
communication we have tried several types of culture media and have identified DCCM-2 as the most suitable culture medium
to generate human MHC-AF. MHC-AF generated in DCCM-2 medium appears to be a protein molecule resistant to pH 2 treatment but
sensitive to heat treatment (56°C × 45 min) and treatment with proteolytic enzymes trypsin and chymotrypsin. 相似文献
17.
R. M. Pitchappan J. N. Agrewala V. Dheenadhayalan J. Ivanyi 《Journal of biosciences》1997,22(1):47-57
More than one mechanism may contribute to disease susceptibility in tuberculosis, viz., major histocompatability complex (MHC)
restriction phenomenon, spectrum of immune reactivity/cytokine profile and epidemiology induced anergy. Experiments from our
laboratories revealed that (i) human leucocyte antigen D-related allele 2 (HLA DR2) predispose for a more severe form of pulmonary
tuberculosis encoding a high responder status, (ii) spectrum of immune reactivity to mycobacteria is ‘innate’, and it is demonstrable
in healthy individuals from endemic area, (iii) there is no correlation between the purified protein derivative (PPD) response
and peptide responses, (iv) once a person is high responder to P16 and P38 derived peptides (6/22), he/she (whether a patient
or control) is a high responder for a wide range of mycobacterial peptides and (v)majority of the T-cell clones generated
in vitro, to peptide 16.3 (amino acids 21–40) of 16 kA a mycobacterial antigen, in an HLA DR2 positive healthy individual is HLA DR
restricted, permissive and of Th1 phenotype. The results suggested that MHC class II restriction play a role in peptide recognition
and the immune response. Nonetheless the outcome and specificity of the immune reactivity and the resultant disease pathogenesis
may depend on the promiscuity of peptide recognition and cytokine profiles. 相似文献
18.
A method has been developed for biospecific interaction analysis between antigen and antibody using solid phase binding approach.
Real time kinetics between monoclonal antibody and human chorionic gonadotropin have been studied. Kinetic constants of the
bimolecular reaction are determined. Affinity constants measured by several independent methods have been found to be relatively
consistent. Convenient and simple procedures to determine affinity constant, Konand Koff of monoclonal antibody-human chorionic gonadotropin interaction using binding of [125I]hCG to immobilized monoclonal antibody are presented. Values obtained compare well with those obtained using surface plasmon
resonance technology, making this method a viable alternative. 相似文献
19.
S. Bhattacharyya S. N. Das A. B. Dey K. Nagarkar J. Lobo S. K. Kapoor H. K. Prasad 《Journal of biosciences》1997,22(1):99-109
Interferon-(IFN-γ) has been considered to be a critical protective immunomodulatory component against
Mycobacterium tuberculosis (M. tb.) infection. In this study T-cell proliferation and IFN-γ production upon stimulation with M. tb. were assessed in
patients of pulmonary tuberculosis and healthy contacts. The studies were based on lymphocyte transformation test and detection
of intracellular IFN-γ production by CD4 + ve T-cells by flowcytometry. Patients showed lower levels of proliferation, the
stimulation index being in the range of 2.17 1.1 (mean + SD) compared to the contacts (SI = 4 59±1.6) (P < 0.01). The kinetics
of intracellular induction of IFN-γ on M. tb. stimulation showed a proportional increase in the CD4 + ve T-cell population.
The increase was maximal between 96–120 h of culture. In healthy contacts the number of IFN-γ expressing CD + ve T-cells increased
to 2.5 to 41 × 104 cells/ml in M. tb. stimulated cultures compared to control cultures (0.1 – 15 × 104). In contrast patients showed no/marginal increase in CD4 + ve T-cell population expressing intracellular IFN-γ Thus the
lack of induction of IFN in CD4 + ve T-cells in patients could be a critical shortcoming in their ability to combat tubercle
bacilli infection. 相似文献
20.
Changes in ovarian follicular kinetics were studied in relation to aging in the Indian skipper frog
Rana cyanophlyctis.Age was determined by skeletochronology, by counting the number of growth rings and lines of arrest of growth from the cross
sections of 4th phalange of 4th toe. For follicular kinetics study oocytes were counted under binocular using 10% of Bouin’s
fixed ovary and they were classified into first growth phase, medium-sized second growth phase, large-sized second growth
phase and atretic follicles.
Analysis of phalangeal cross sections indicated that frogs ranging 14–54 g in body weight and 4.9–8.9 cm in body size showed
1–7 year rings. Frogs that weighed 14–16 g showed 1 year ring, and contained immature ovaries; those with 18 g body weight
had one to two year rings, in which second growth phase oocytes appeared for the first time in the primiparous ovary. Frogs
with 20–54 g body weight showed 2–5 year rings in which ovary contained 5–24% of second growth phase oocytes. Further, body
weight, body size, ovarian weight, number and size of second growth phase oocytes and total number of oocytes showed a significant
(P < 0.05) positive correlation, while, the number of first growth phase and atretic follicles showed a poor correlation with
age.
The results suggest that in nature, the age of
Rana cyanophlyctis
ranges between 1–7 years. Phalangeal growth rings are formed annually. Females attain sexual maturity in 2nd year. Frogs with
2–5 years of age may constitute breeding females. Body weight, body size, ovarian mass, number of second growth phase and
total oocytes, and egg size increase with age up to 5 years. 相似文献