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Biomedical subjects

R Srinivasan

Publications and source records attributed to R Srinivasan.

At least 145 records · Page 8Linked to original sources
PubMed1993

Diresidue-monopeptide (DRMP) model for analysis of peptide and protein conformation.

The paired torsional angle representation phi i, psi i in protein conformational analysis is only one type of correlation with a focus on a given C alpha residue and gives the relative orientation of a pair of peptide planes sandwiching a given residue (referred as mono-residue dipeptide model, MRDP). A shift of emphasis from a residue site to a given peptide plane (termed as diresidue monopeptide model, DRMP) leads to examination of pairs such as phi i, psi i-1 and other parameters derived therefrom. General sum (alpha n = phi i + psi i-n) and the difference (beta n = phi i - psi i-n) parameters are introduced, of which, n = 0 and n = 1 relate to MRDP models and DRMP models respectively. Apart from the helical regions, where 'alpha 0' is found to be relatively stable, the sum parameters have been found to be more useful in the analysis of beta-turns. The 'alpha 0' at the second and third residue sites and 'alpha 1' at the middle peptide plane of the four residue corner is found to offer a numerical triplet code for resolving various beta-turn types. Besides these, an additional parameter introduced under the DRMP model is a virtual torsion angle 'sigma 1' involving C beta i-1 ... C'i-1 - Ni ... C beta i, which is expected to reflect the effect of interaction of the side chain atoms. The sigma 1, alpha 1 pair is found to play a role parallel to phi, psi at a given residue site.(ABSTRACT TRUNCATED AT 250 WORDS)

Dipeptides↗
PubMed1993

A unique or essentially unique single parametric characterisation of biopolymeric structures.

A generalised method of characterising the three dimensional structure of any biopolymer is proposed. The method makes use of rotation and superposition of identical rigid monomeric units that comprise the polymer. Out of the various parameters involved (refers the seven parametric representation of relating two identical rigid bodies in space), the angle of rotation and superposition termed as 'phi s' turns out to be essentially unique. An ideal biopolymer with n identical rigid units is characterised by (n-1) such unique angles. In applying the results to real biopolymers, the importance of recognising that monomeric units are no more rigid but only quasi-rigid is emphasised. However, by appropriate choice of 'rigid' fraction of the quasi-rigid monomers, one is led, as first approximation, to essentially unique characterisation of the biopolymer with (n-1) such unique angles. The phi s as a function of residue number acts essentially as a finger print of the given polymeric fold and the conformation of the chosen biopolymer. However, the full set of seven parameters are needed for model building. It is emphasised that the method is general in its application to any polymer and the application of the results to proteins and nucleic acids is illustrated.

Amino Acids↗
PubMed1993

Laboratory observations on the biology of the phlebotomid sandfly, Phlebotomus papatasi (Scopoli, 1786).

Investigations on the biology of Phlebotomus papatasi were carried out under laboratory conditions at 28 +/- 2 degrees C and 80 +/- 1% RH. Fecundity of the female varied between 61 and 48 (mean 56.2 +/- 5.46) and the incubation period of eggs ranged from 7-9 (mean 7.81 +/- 0.61) days. The developmental duration of larvae and pupae varied from 24 to 31 (mean 28.57 +/- 2.71) and 9 to 11 (mean 10.38 +/- 1.51) days, respectively. The rate of insemination, determined from the females that laid fertile eggs, was found to be maximum when the females were three days old. Autogeny was observed from female sandflies, emerged from the larvae fed on animal liver powder. The duration of first and second gonotrophic cycles under ambient conditions was shortest in summer and longest in winter. Studies on adult longevity showed that the females fed on mouse blood survived for 6 to 27 days (mean 14 +/- 12.5 days).

Age Factors↗
PubMed1992

Preparation of TEM foils from Nb-10 a/o Si.

Ductile phase toughened composites contain phases with significantly different physical properties. Consequently, these phases thin at different rates depending on the sample preparation procedure. A new TEM foil preparation method for the ductile phase toughened Nb-10 a/o Si material has been developed. The method involves chemical thinning in a 70% nitric acid/30% hydrofluoric acid solution followed by electropolishing in a 12.5% sulfuric acid/87.5% methanol electrolyte at -40 degrees C. This procedure for making TEM foils results in large thin areas with the minimum of artifacts. Mechanical grinding of a sample followed by either ion milling, dimpling, or electropolishing produced foils with large electron transparent areas, but with uncharacteristic features of the original Nb-10 a/o Si alloy microstructure. These artifacts were identified as dislocations, surface mottling, and antiphase domains.

Alloys↗
PubMed1992

A slow obligatory proton release step precedes hydride transfer in the liver glutamate dehydrogenase catalytic mechanism.

We have used the stopped-flow indicator dye method to measure proton release and product formation simultaneously in the initial transient-state portion of the glutamate dehydrogenase-catalyzed oxidative deamination of L-glutamate. We observe a measurably slow release of a proton from the enzyme-NADP-L-glutamate complex. This proton release precedes the hydride transfer step, as indicated by the distinct lag in the product formation signal. We show that the proton release step corresponds to an obligatory intermediate in the reaction sequence. We also find that compounds which are competitive inhibitors of L-glutamate are capable of inducing this phenomenon. We prove that this unanticipated prehydride transfer event cannot be due to the release of an alpha-amino group proton from the substrate.

Animals↗
PubMed1992

Popliteal embolectomy: does it still have a role?

The failure of a femoral embolectomy presents a difficult problem. The role of popliteal embolectomy in the subsequent management is still not clear. A study of 12 patients who underwent a secondary popliteal embolectomy is reported. Nine of the 12 patients had successful results in terms of limb salvage. The question that has to be addressed is the role of popliteal embolectomy as opposed to thrombolysis. Recent studies tend to favour the latter approach. It is concluded that if an embolectomy catheter will not pass or will not clear the distal segment, the surgeon should consider intraoperative thrombolysis or popliteal embolectomy prior to embarking on a bypass procedure.

Amputation, Surgical↗
PubMed1992

Biting rhythm & biting activity of phlebotomid sandflies.

The biting behaviour of Phlebotomid sandflies was studied in a rural village of Pondicherry through all night collections for a period of one year, using human volunteers and cattle as baits. Phlebotomus papatasi was caught only on human bait, showing anthropophily while Ph. argentipes was caught on cattle baits, showing zoophily. The biting activity was seen throughout the night, reaching a peak of 0100 h in Ph. papatasi and 0200 h in Ph. argentipes.

Animals↗
PubMed1992

An improvised method of laboratory colonization of Phlebotomus papatasi, the vector of cutaneous leishmaniasis.

A cyclic colony of P. papatasi was successfully established, using wild caught females. The major obstacle in the colonization was infestation of fungus, which was solved when bentonite, a dehydrant was mixed in the larval diet i.e., powdered and sterilized faecal pellets of rabbit. The average duration of development from egg to adult was 46.41 +/- 3.26 days. Females readily engorged on mouse, which was kept immobilized inside restrainer cages Majority of the fed females laid viable eggs, when confined in improvised styro-foam humidity chambers and survived after oviposition. In this process a stable, cyclic colony was established and it is now in F39 generation.

Animals↗
PubMed1992

Seasonal abundance, natural survival & resting behaviour of Phlebotomus papatasi (Diptera: Phlebotomidae) in Pondicherry.

A study was carried out on the seasonal abundance, natural survival and resting behaviour of Ph. papatasi in four ecologically different areas of Pondicherry. The average indoor resting density ranged from 2.25 (May 1989) to 16.70/man hour (October 1989). Ph. papatasi was observed to be predominantly endophilic in its resting behaviour. A significant positive correlation was observed between rainfall and relative density. The daily survival of adult population ranged from 0.893 to 0.949 and showed significant positive correlation with relative humidity. Examination of the abdomen of indoor resting females showed that the entire period of gonotrophic cycle was spent indoors.

Animals↗
PubMed1992

Identification of bloodmeals of phlebotomine sandflies using the agarose gel diffusion method.

The source of blood meal of wild caught Phlebotomid sandflies collected in areas around Pondicherry was identified using an agarose gel diffusion method. A total of 497 blood samples obtained from freshly engorged Phlebotomid sandflies were tested. Of these 66.8% were positive to human antisera, 29.2% to bovine antisera and the remaining 4.0% to avain antisera. The human blood indices of P. papatasi and P. argentipes were 0.91 and 0.04, respectively.

Animals↗
PubMed1991

The effect of changes in gramicidin conformation on bilayer lipid properties.

The effects of two different gramicidin conformations on lipid phase behaviour and dynamics are compared. Samples of chain-perdeuterated dimyristoylphosphatidylcholine containing gramicidin were first prepared with gramicidin in a state having a circular dichroism spectrum generally identified as corresponding to the non-channel conformation. The effects, on bilayer lipid properties, of gramicidin in this conformation were then determined using deuterium nuclear magnetic resonance measurements of acyl chain orientational order and transverse relaxation times as a function of temperature. These samples were then incubated at 65 degrees C to convert the gramicidin to a state with a circular dichroism spectrum of the type generally identified with the channel conformation. The nuclear magnetic resonance measurements were then repeated. In the gel phase, it was found that transverse relaxation time and chain orientational order of the lipid were insensitive to gramicidin conformation. In the liquid crystalline phase, gramicidin in the channel conformation was found to have a slightly larger effect on transverse relaxation and orientational order than gramicidin in the non-channel conformation. The perturbation of the phase behavior by gramicidin was found to be relatively insensitive to gramicidin conformation.

Circular Dichroism↗
PubMed1991

Characterization of the general anion-binding site in glutamate dehydrogenase-NADPH complex.

The reductive amination of alpha-ketoglutarate, catalyzed by bovine liver glutamate dehydrogenase, is inhibited by various anions. Formate and acetate ions are competitive with alpha-ketoglutarate. The pH dependence of the pKi profiles for these anions reveals that they bind to the enzyme-NADPH complex only when an enzymatic residue of pK 8.0 +/- 0.1 in the binary complex is protonated. The ionization of this residue has a delta Hion of 15 +/- 4 kcal/mol. These pK and delta Hion values are not significantly different from those observed in the same complex for the enzyme group which binds the gamma-CO2- of alpha-ketoglutarate and oxalylglycine. It is concluded that formate and acetate also bind to the gamma-carboxylate site in enzyme-NADPH. The Ki values for formate and acetate in a buffer containing 0.1 M phosphate are 20 +/- 4 and 32 +/- 5 mM, respectively, when the pK 8.0 group is fully protonated. Phosphate and trifluoroacetate also show an inhibitory effect, while valerate and sulfate have little effect on the reductive amination rates. The results suggest that specific anions can bind to the gamma-carboxylate site by ionic interactions and alter the kinetic and thermodynamic parameters of the glutamate dehydrogenase-NADPH complex in significant ways.

Acetates↗
PubMed1991

Thermodynamic parameters for the glutamate dehydrogenase catalyzed alpha-imino acid-alpha-amino acid interconversion.

Delta 1-Piperidine 2-carboxylic acid, an alpha-imino acid, is reduced by 1,4-dihydropyridines to pipecolic acid, an alpha-amino acid, and the corresponding pyridinium ions. This nonenzymatic reaction occurs only in the direction of pipecolic acid production. Glutamate dehydrogenase catalyzes this reaction when the reductant is NADPH and gives as products L-pipecolic acid and NADP+. The reaction velocity for the enzyme-catalyzed reaction is measurable in either direction. The pH-independent equilibrium constant, Keq, for the reduction of the imino acid by NADPH to give pipecolic acid anion and NADP+ was determined from the equilibrium conditions and the pKa values of pipecolic acid (10.72) and of the cyclic imino acid (8.10). The value of Keq was found to be 175 +/- 30; the values of delta G0, delta H0 and delta S0 are -3.1 +/- 0.1 kcal/mol, 5 +/- 1 kcal/mol and 27 +/- 4 e.u., respectively. The data indicate that the reactants are far more solvated than the products and that there must be a large degree of solvent reorganization during the course of the reaction. If these thermodynamic parameters apply to the redox step of the enzyme-catalyzed glutamate reaction, then the burst phase which results upon mixing the enzyme, L-glutamate and NADP+ in stoichiometric amounts must contain a hidden nonredox step of large delta H0 value to account for the curved Arrhenius plot observed for this phase (A.H. Colen, R.T. Medary and H.F. Fisher, Biopolymers 20 (1981) 879).

Amino Acids↗
PubMed1991

Spectrum of oculomycosis in South India.

Ninety-one consecutive cases of proven oculomycosis were studied in relation to clinical features and epidemiological parameters. Mycotic corneal ulcers formed the major group (76%), followed by endophthalmitis (20%). Aspergillus was the common causative fungus (36%) in keratomycosis followed by Penicillium species (29%). Fusarium keratomycosis was not as common as reported in the literature. In endophthalmitis there was preponderance of Penicillium as the causative fungus. These etiological agents are studied in comparison with studies of conjunctival flora of healthy controls and culture studies of common objects of trauma. Mycotic endophthalmitis was seen following cataract surgery in 64% of cases. Contrary to expectations the onset of endophthalmitis was within 2 weeks of surgery in most cases. Trauma with organic matter was an important predisposing factor in keratomycosis. These observations are discussed in relation to the clinical features. Other unusual forms of oculomycosis are also discussed.

Adolescent↗