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Biomedical subjects

V Sitaramam

Publications and source records attributed to V Sitaramam.

At least 37 records · Page 2Linked to original sources
PubMed1989

Variable porosity of the mitochondrial inner membrane induced by energization.

The empirically observed relationship between the activity of membrane-bound enzyme systems and transporters and the external osmotic pressure offered a direct method to assess the reflection coefficients to polyols in respiring mitochondria. These osmotically modulated reaction rates varied with the molecular mass of the external polyol similar to volume and solute fluxes across dialysis membranes. The equivalent pore radii of mitochondria were shown to increase with respiration (and temperature) and decrease on addition of the uncoupler, 2,4-dinitrophenol. The magnitude of the induced porosity in the inner membrane was large enough to render the chemiosmotic mechanism inoperable in well-coupled rat liver mitochondria.

2,4-Dinitrophenol↗
PubMed1989

Differential effects of osmotic pressure on mitochondrial respiratory chain and indices of oxidative phosphorylation.

Oxidative phosphorylation was critically evaluated in terms of activities which are sensitive and insensitive to variations in external osmotic pressure in mitochondria. Integrity of mitochondria was determined in terms of a variety of parameters, including the latency of the occluded enzymes, by careful titrations as a function of external osmotic pressure as well as detergent concentrations. The evidence indicated that the rate-limiting step in respiratory states 2 and 4 would be osmotically insensitive, as opposed to the osmotically sensitive respiration of states 1 and 3 and uncoupler-stimulated respiration with glutamate + malate and succinate. Cytochrome oxidase activity in mitochondria as well as in purified reconstituted systems exhibited osmotic insensitivity but marked sensitivity to ionic strength, offering an interesting model to study the osmotically insensitive respiration. Cytochrome oxidase activity led to permeation of mannitol across the mitochondrial inner membrane. Stimulation of cytochrome oxidase activity by uncouplers did not require an intact membrane.

2,4-Dinitrophenol↗
PubMed1989

Genetic code preferentially conserves long-range interactions among the amino acids.

The physical properties of amino acids were investigated in order to evaluate their possible relationship to the assignment of codons for amino acids in the genetic code. A comparison of the interconversion probability between amino acids and the distances between the amino acids for individual physical properties revealed a striking hierarchy among the physical properties. Surprisingly, it is the long-range/solvent interactions and not the short-range/stereochemical properties which are preferentially conserved in the genetic code.

Amino Acids↗
PubMed1988

ATP hydrolysis induces variable porosity to mannitol in the mitochondrial inner membrane.

Osmotic titration of ATPase activity in rat liver mitochondria was consistent with enhanced porosity of the mitochondrial inner membrane to mannitol due to ATP hydrolysis even when endogenous respiration was inhibited by rotenone. The occluded ATPase activity, which exhibits osmotic activation with an optimum near isotonicity, depends both on the ATPase activity per se and on the activity of the ADP/ATP carrier. Purified ADP/ATP carrier incorporated into small, unilamellar liposomes was critically shown to exhibit dependence of its activity on the osmotic pressure differences across the membrane, with maximal activity corresponding to isotonicity, regardless of the actual internal tonicity.

Adenosine Triphosphate↗
PubMed1987

Diagnostic and prognostic value of RNA-proteolipid in sera of patients with malignant disorders following therapy: first clinical evaluation of a novel tumor marker.

The circulating level of a novel RNA-proteolipid complex associated with malignant diseases was critically evaluated as a tumor marker in clinical oncology. The complex, isolated from the sera of cancer patients, exhibited unvarying chemical composition regardless of the cell type and clinical staging. Clearance from blood was rapid with a half-life of approximately 2 days. Tumor mass could be correlated with the circulating level. After effective treatment the level fell and rose again 10 months prior to the conventional clinical diagnosis of relapse.

Biomarkers, Tumor↗
PubMed1986

Anomalous permeability and stability characteristics of erythrocytes in non-electrolyte media.

The permeability characteristics of the erythrocyte membrane were critically evaluated in electrolyte and non-electrolyte (sucrose) media by ion-selective electrodes and radioactive polyol fluxes as well as by the novel technique of osmometry. K+ efflux demonstrated a linear osmotic susceptibility distinct from Na+ influx upon incubation in NaCl media of various tonicities. In non-electrolyte media, acidification of the medium, large fluxes of K+, sucrose and even haemoglobin (as manifest by hypertonic disruption) were consistent with enhanced porosity of the bilayer due to the field created by surface charge density leading to density fluctuations in the bilayer.

Animals↗
PubMed1986

Enzyme-linked immunolysis assay for tumour-specific surface antigens.

Expression of the activity of the cytosolic enzyme lactate dehydrogenase released on cell lysis by tumour specific antibodies in the presence of complement was investigated by direct assay of the expression of the occluded enzyme in tumour cell suspensions. This method, called Enzyme Linked Immunolysis Assay (ELILA) was shown to be more sensitive than conventional cytotoxic assays. The data fit well in the linear regression model, so that the technique can be used for quantitation of the antibody titres.

Animals↗
PubMed1986

Ubiquinone-8 stimulates phagocytosis in macrophages by modulation of the kinetics of the Fc receptor.

The effect of exogenous ubiquinone-8 (Q8) on IgG- and C3b-mediated phagocytosis of sensitized sheep red blood cells and of opsonized Staphylococcus aureus by macrophages was studied by morphological and quantitative methods. Q8 stimulated the initial events of phagocytosis, that is, attachment and ingestion, in which occupancy of the Fc receptor by IgG was shown to be of critical significance. The kinetics of competitive inhibition of phagocytosis of opsonized bacteria by macrophages by using Fc fragments suggested the intimate role of the kinetics of the Fc receptor in the initial events of phagocytosis and, further, the modulation of the kinetics of the Fc receptor by Q8 as the basis of enhanced phagocytosis by Q8.

Animals↗
PubMed1985

Respiration induces variable porosity to polyols in the mitochondrial inner membrane.

The osmotic basis of low and high amplitude swelling in mitochondria was investigated in detail using sucrose and mannitol as external osmolytes. Osmotic behaviour of mitochondria in various respiratory states was consistent with significant changes in the porosity of the inner membrane corresponding to the rate of respiration. The stoichiometry of oxidative phosphorylation was confirmed to be dependent on the physical state (i.e., osmotic stretch) of the inner membrane regardless of the external polyol used. High amplitude swelling in polyol media was shown to arise from a sequential disruption of the outer and inner mitochondrial membranes, due to a dynamic instability induced by a combination of respiration, unscreened (fixed) surface charge density and the consequent variable porosity of the inner membrane. These novel experimental findings based on the physical theory of osmosis emphasize the need to define the fine structural changes of the inner membrane associated with oxidative phosphorylation to arrive at a comprehensive mechanism.

Animals↗
PubMed1983

Studies on the non-linear osmotic pressure-volume relationship in mitochondria and entry of sucrose into the matrix space during centrifugation.

The two-compartment sucrose-space hypothesis was refuted recently (Sitaramam, V. and Sarma, M.K.J. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 3441-3445), using the novel technique of enzyme osmometry of matrix enzymes based on the following premise: a shift in the discontinuity (break-point) of the activity profile of an occluded enzyme as a function of external osmolarity (i.e., osmotic profiles) would imply a shift in the internal solute content of the same compartment as that of the enzyme. A systematic re-evaluation of the osmotic profiles of mitochondrial enzyme systems has revealed that the activities of several matrix and inner membrane enzyme systems exhibited break-points larger than those of osmolysis (i.e., actual release of marker enzymes into the medium) of mitochondria. The experimental findings were consistent with (i) entry of sucrose across the inner membrane consequent to enhanced permeability effects by gravitational field, and (ii) dependence of the kinetic constant of several membrane-bound enzymes/carrier proteins, respiratory coupling and ADP/O ratio on the volume of mitochondria (i.e., osmotic stretch of the inner membrane).

Animals↗
PubMed1981

Gravitational field enhances permeability of biological membranes to sucrose: an experimental refutation of sucrose-space hypothesis.

Isotonic conditions for the integrity of subcellular organelles are shown to be remarkably influenced by the concentration of sucrose present during their isolation by centrifugation. Using the technique of enzyme osmometry, we show that the content of sucrose in synaptosomes reflects nearly total equilibration across the membrane during centrifugation, due to altered permeability of membranes. Presence of sucrose in the matrix space of mitochondria, as demonstrated by enzyme osmometry of matrix enzymes, indicates that the sucrose-space hypothesis is invalid.

Animals↗