Effect of sublethal levels of nitrite on some blood parameters of juvenile Labeo rohita (Hamilton-buchanan)

Juveniles of L. rohita were exposed to sublethal levels of nitrite (0.02, 0.1 and 0.4 mg/l) for 2, 24, 48 and 96 hr. The time of exposure at individual concentrations of nitrite did not show any significant difference in haemoglobin, cortisol, chloride and lactic acid. Haematocrit showed significant reduction with increasing concentration of nitrite irrespective of duration of exposure. Fishes exposed to 0.4 mg/l nitrite showed significantly high levels of glucose beyond 2 hr. The mean erythrocytic fragility of fishes exposed to the 3 concentrations of nitrite for 3 exposure periods showed significant higher sensitivity to osmotic stress. The results suggest decrease in haematocrit and cell wall strength of erythrocytes creating stress to fish.     

A semiparametric mixture model for analyzing clustered competing risks data

A very general class of multivariate life distributions is considered for analyzing failure time clustered data that are subject to censoring and multiple modes of failure. Conditional on cluster-specific quantities, the joint distribution of the failure time and event indicator can be expressed as a mixture of the distribution of time to failure due to a certain type (or specific cause), and the failure type distribution. We assume here the marginal probabilities of various failure types are logistic functions of some covariates. The cluster-specific quantities are subject to some unknown distribution that causes frailty. The unknown frailty distribution is modeled nonparametrically using a Dirichlet process. In such a semiparametric setup, a hybrid method of estimation is proposed based on the i.i.d. Weighted Chinese Restaurant algorithm that helps us generate observations from the predictive distribution of the frailty. The Monte Carlo ECM algorithm plays a vital role for obtaining the estimates of the parameters that assess the extent of the effects of the causal factors for failures of a certain type. A simulation study is conducted to study the consistency of our methodology. The proposed methodology is used to analyze a real data set on HIV infection of a cohort of female prostitutes in Senegal.     

A note on the estimation of microbial glycosidase activities by dinitrosalicylic acid reagent

 In the estimation of glycosidase activity by dinitrosalicylic acid (DNS) reagent, the stoichiometry of DNS reduction was reported to increase proportionately with the increase in the number of glycosidic linkages present in oligosaccharides liberated by the enzyme. The relationship between increases in DNS reduction and increases in the number of glycosidic bonds was found to be represented by a part of a rectangular hyperbola. The increase was optimum with disaccharide and insignificant when the degree of polymerization (DP) was ≥10. The difference did not arise as a result of the DNSA discriminating between mono- and oligosaccharide oxidation. The relationship stemmed from the acidity of the hydroxyl group adjacent to the reducing group, which repressed DNS reduction. The acidity is likely to decrease with an increase in oligosaccharide chain length. It is suggested that DNS reduction is actually optimum and uniform for all oligosaccharides of DP ≥ 10 and that it is minimum for monosaccharide. Thus the introduction of rectification factors in the estimation of glycosidase activities by the DNS method appears to be justified. Received: 18 January 1999 / Received revision: 7 December 1999 / Accepted: 19 December 1999     

Design and synthesis of a novel enediynyl pentapeptide with predominantly beta-turn structural motif and its potential as a fluorescence-based chemosensor

A novel enediynyl pentapeptide in the protected form 1 was synthesized and characterized. It exists predominantly in beta-turn structural motif as revealed by variable temperature NMR and CD spectroscopy. In the presence of transition metal ions and gold nanoparticles, the fluorescence intensity of the peptide got enhanced with remarkable quantum yield with the Z-enediynyl -amino acid acting as a fluorophoric reporter. The interesting photophysical behaviors with alkali and alkaline earth metal ions are also reported.     

Recurring Plankton Bloom Dynamics Modeled via Toxin-Producing Phytoplankton

A simple nutrient–phytoplankton model is proposed and analyzed in the presence of toxic chemicals released by toxin-producing phytoplankton (TPP) to understand the dynamics of seasonally recurring bloom phenomena. We observe that the presence of toxic chemicals helps to explain the bloom phenomenon. We have further studied our proposed system by varying the toxin liberation rate. Our model displays a wide range of dynamical behaviours, from simple cyclical blooms to irregular chaotic blooms. We also observe skipping phenomenon. The effect of toxic chemicals released by TPP cannot, thus, be ignored in ‘bottom-up’ models. J. Chattopadhyay is supported by the Ministry of Foreign Affairs Indo-Italian program of cooperation in Science and Technology, “Biomedical Sciences”. S. Chatterjee is supported by Ministero dell’Istruzione, dell’Università e della Ricerca, Bando per borse a favore di giovani ricercatori indiani. S. Chakraborty is supported by the Council of Scientific and Industrial Research, Human Resource Development Group, New Delhi.     

S6 Peptide Derived from KvAP Channel Shows Cooperativity in Gating on Bilayer Lipid Membrane

Collective behavior of S6 peptide channels derived from KvAP (a bacterial potassium channel) incorporated in lipid bilayer membrane, has been investigated at various applied potentials through multi-channel electrophysiological experiments. The current versus time traces at any particular membrane potential show clear steps for sequential opening of the multi-channels. The minimum current (representing one-channel current) was found out from the amplitude histograms. Accordingly, the number of open channels corresponding to a particular open state was calculated. It was observed that the above-mentioned one channel current is higher than the corresponding single-channel current at most of the applied membrane potentials. Moreover, the difference between the single and one channel conductances is a nonlinear function of the membrane potential. We conclude that the S6 multi-channels show co-operative gating. Voltage relaxation studies support the above-mentioned conclusion.     

Characterisation of antimony-resistant Leishmania donovani isolates: biochemical and biophysical studies and interaction with host cells

Recent clinical isolates of Leishmania donovani from the hyperendemic zone of Bihar were characterised in vitro in terms of their sensitivity towards sodium stibogluconate in a macrophage culture system. The resulting half maximal effective concentration (EC(50)) values were compared with those of known sensitive isolates. Fifteen of the isolates showed decreased sensitivity towards SSG with an average EC(50) of 25.7 ± 4.5 μg/ml pentavalent antimony (defined as antimony resistant), whereas nine showed considerable sensitivity with an average EC(50) of 4.6 ± 1.7 μg/ml (defined as antimony sensitive). Out of those nine, seven were recent clinical isolates and the remaining two were known sensitive isolates. Compared with the antimony sensitive, resistant isolates showed enhanced expression of thiol metabolising enzymes in varying degrees coupled with increased intracellular non-protein thiol content, decreased fluorescence anisotropy (inversely proportional with membrane fluidity) and over-expression of the terminal glycoconjugates (N-acetyl-d-galactosaminyl residue). Macrophages infected with resistant but not with sensitive showed up-regulation of the ATP Binding Cassette transporter multidrug resistance protein 1 and permeability glycoprotein, while the supernatant contained abundant IL-10. The above results reinforce the notion that antimony resistant parasites have undergone a number of biochemical and biophysical changes as part of their adaptation to ensure their survival in the host.     

Multiple viral infection in Penaeus monodon shrimp postlarvae in an Indian hatchery

Moribund Penaeus monodon postlarvae (PL8-PL10) in a hatchery in India were found to be simultaneously infected by 3 different viruses. They were highly infected with monodon baculovirus (MBV) and hepatopancreatic parvovirus (HPV) by histology and with white spot syndrome virus (WSSV) by non-nested polymerase chain reaction (PCR). Apparently healthy postlarvae tested from the same hatchery were positive for MBV and WSSV by nested PCR only. Tissue sections of such postlarvae did not show any histopathological changes. The simultaneous occurrence of these 3 viruses in hatchery-reared postlarval P. monodon is being reported for the first time.