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Biomedical subjects

R Venkatesh

Publications and source records attributed to R Venkatesh.

At least 19 recordsLinked to original sources
PubMed2002

RecX protein abrogates ATP hydrolysis and strand exchange promoted by RecA: insights into negative regulation of homologous recombination.

In many eubacteria, coexpression of recX with recA is essential for attenuation of the deleterious effects of recA overexpression; however, the molecular mechanism has remained enigmatic. Here, we show that Mycobacterium tuberculosis RecX binds directly to M. tuberculosis RecA as well as M. smegmatis and E. coli RecA proteins in vivo and in vitro, but not single-stranded DNA binding protein. The direct association of RecX with RecA failed to regulate the specificity or extent of binding of RecA either to DNA or ATP, ligands that are central to activation of its functions. Significantly, RecX severely impeded ATP hydrolysis and the generation of heteroduplex DNA promoted by homologous, as well as heterologous, RecA proteins. These findings reveal a mode of negative regulation of RecA, and imply that RecX might act as an anti-recombinase to quell inappropriate recombinational repair during normal DNA metabolism.

Adenosine Triphosphate↗
PubMed1999

Light regime, riboflavin, and pH effects on 2,4-D photodegradation in water.

A laboratory study was conducted to determine the effects of light regime, riboflavin, and pH on photodegradation of 2,4-D in aqueous solution. In controlled-environment chamber experiments, riboflavin sensitized 2,4-D photolysis in a concentration-dependent manner under both attenuated UV (-UV) and enhanced UV (+UV) light regimes. The photolysis half-life of 2,4-D in solutions containing 10 mg L-1 riboflavin was 9.7 and 12.5 h when exposed to +UV and -UV, respectively, compared to no photolysis in the absence of riboflavin. In contrast, the extrapolated half-life of 2,4-D in solutions containing 2.5 mg L-1 riboflavin was 46 h under +UV and 72 h under -UV. The rate of 2,4-D photolysis in the presence of riboflavin increased under both light regimes as initial pH of the solution was decreased from 7.5 to 4.5. The half-life of 2,4-D in the presence of 10 mg L-1 riboflavin at pH 4.5 and exposed to +UV was 1.6 h. Lumichrome, a principal photoproduct of riboflavin, did not photosensitize 2,4-D. Concentrations of 2,4-dichlorophenol formed as a result of riboflavin-sensitized 2,4-D photolysis were higher under the -UV than the +UV regime. These results indicate that riboflavin concentration, solution pH, and light regime are interacting factors that may be manipulated to enhance rates of aqueous 2,4-D photolysis.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1998

Modulation of stability properties of bovine trypsin after in vitro structural changes with a variety of chemical modifiers.

Controlled chemical modification of enzymes, targeting groups not involved in the active site, can lead to modified catalysts that are intrinsically more efficient and resistant to heat and denaturing agents. Bovine pancreatic trypsin was covalently modified up to 75-85% with monomeric glutaraldehyde (MGA), polymeric glutaraldehyde (PGA), oxidized sucrose and oxidized sucrose polymers (OSP 70 and OSP 400). Virtually no loss in activity occurred upon modification. Temperature optima of trypsin shifts from 45-76 degrees C and T50 from 54-76 degrees C for the best modified sample made with OSP. The efficiency of the modifiers in stabilization was ranked in the order: OSP 400-T > OSP 70-T > PGA-T > MGA-T > Sucrose-T. Half-life of modified enzymes also followed the same trend. Both stabilization factor and t1/2 decreased with increasing temperatures. The free energy of activation for inactivation delta(deltaG*) varies from 12-20 kJ/mol and the activation enthalpy delta(deltaH*) of the modified trypsin by 80-120 kJ/mol indicating stabilization. Inactivation of modified trypsin by urea is less noticeable. The character of the two-step inactivation process of trypsin changes with the degree of stabilization in that the duration of phase I one increased noticeably as stabilization increases. Native trypsin fluoresces less intensely showing a red shift under the influence of denaturation. Such a fluorescence change is not so obvious for the modified enzymes indicating conformational stability acquired by modification.

Animals↗
PubMed1998

Retardation of thermal and urea induced inactivation of alpha-chymotrypsin by modification with carbohydrate polymers.

Modification of enzymes by means of covalent coupling using soluble polymers results in enzymes which retain high biological activity and display resistance to denaturants, high temperature and chaotropic agents. Alpha-chymotrypsin, which has a potential for use in industrial applications, was covalently modified by reductive alkylation using polymeric sucrose (OSP, molecular weight 70 and 400 kDa), dextran (73 and 250 kDa) and carboxymethyl cellulose (CMC, approximately 12 kDa). The derivatives retained around 50-80% activity depending on the polymer used and the extent of modification. At the same time, they displayed better thermotolerance than their native counterpart with 4-14 degrees C higher T50 values. During thermal inactivation, both the native and modified enzymes showed biphasic inactivation kinetics. Half-life of modified enzymes were 2-66-fold greater for the first phase and 5-250-fold greater than the native for the second phase of inactivation. The activation free energy of inactivation of alpha-chymotrypsin coupled to polymeric sucrose (400 kDa) was 112.85 kJ/mol for the first phase and 114.71 kJ/mol for the second phase, whereas in the case of the native enzyme, the value for the first phase was 101.55 kJ/mol and 103.42 kJ/mol for the second phase. The activation free energy of inactivation (deltaG*), as well as the activation enthalpy values (deltaH*) of all the modified enzymes were greater than those of the native enzyme, which is an indication of stabilization of the protein and a retardation of inactivation that is usually accompanied by unfolding under thermal and chemical stress. The stability of modified alpha-chymotrypsin is in the following order: OSP 400-C > OSP 70-C > CMC-C > Dextran 73-C = Dextran 250-C.

Carboxymethylcellulose Sodium↗
PubMed1998

Radiation therapy in pseudotumour haemarthrosis.

Total or partial deficiency of factor VIII and IX in the coagulation cascade leads to haemophilia. Haemophilia affecting weight-bearing joints gives a 'pseudotumour' or haemarthrosis-like condition. Surgery and cryoprecipitate infusions have been the treatment for this condition. Radiocolloids and radiation therapy have been used with some benefit. One case of ankle pseudotumour which was treated by low-dose external beam radiation is presented here.

Adolescent↗
PubMed1997

Evaluation of a miniaturized thermal biosensor for the determination of glucose in whole blood.

A miniaturized thermal biosensor has been evaluated as part of a flow-injection analysis system for the determination of glucose in whole blood. Glucose was determined by measuring the heat evolved when samples containing glucose passed through a small column with immobilized glucose oxidase and catalase. Samples of whole blood (1 microliter) can be measured directly, without any pretreatment. The correlation in the response between the thermal biosensor, the Reflolux S meter (Boehringer Mannheim), the Granutest 100 glucose test kit (Merck Diagnostica) and the Ektachem (Kodak) instrument was evaluated. The influence of the hematocrit value and of possible interferences is reported. The correlation measurements show that the thermal biosensor calibrated with aqueous glucose standards generally gives lower values on blood glucose than the reference methods calibrated for serum or blood measurements. Mean negative biases range from 0.53 to 1.16 mmol/l. Differences in sample treatment clearly complicate comparisons and the proper choice of reference method. There was no influence from substances such as ascorbic acid (0.11 mmol/l), uric acid (0.48 mmol/l), urea (4.3 mmol/l) and acetaminophen (0.17 mmol/l) on the response to 5 mmol/l glucose. The hematocrit value does not influence the glucose determination, for hematocrit values of between 13 and 53%.

Biosensing Techniques↗
PubMed1993

Personality and depression in Parkinson's disease.

The Parkinson's disease (PD) patient has been characterized as having a distinctive personality with introverted features. These personality traits are said to predate motor symptoms and are theorized to serve as a subtle clue to latent PD. To examine this hypothesis, we compared remote and current personality features in 35 PD subjects and 35 controls. Subjects' spouses completed a personality inventory (PI) characterizing patients' premorbid and current status. The premorbid PI of PD subjects differed from that of controls in being more "quiet," "generous," "cautious," and "even-tempered," and less "flexible." The characterization of the PD subjects' current personality differed greatly from reported premorbid personality features, i.e., significant change in 13 of 24 PI items. Personality inventory responses regarding both the PD subjects' premorbid and current personality correlated to symptoms of depression and disease severity. Cognition, tobacco use, alcohol consumption, and rural versus urban residency did not correlate with PI responses. We conclude that PD patients are apt to be viewed as introverts premorbidly, and, with disease onset, more striking personality changes are recognized. These perceptions appear to be closely linked to depressed affect and correlate with motor impairment to a lesser extent.

Alcohol Drinking↗
PubMed1993

Serial nonenhancing magnetic resonance imaging scans of high grade glioblastoma multiforme.

Magnetic resonance imaging (MRI) from clinical experience has proven to be superior to all other diagnostic imaging modalities, including computed tomography (CT) in the detection of intracranial neoplasms. Although glioblastoma multiforme presents a challenge for all diagnostic imaging modalities including MRI, MRI is paramount to CT in detecting subtle abnormal water accumulation in brain tissue caused by tumor even before there is disruption of the blood brain barrier. Currently, clinical research and investigational trials on nonionic gadolinium contrast agents have proven that nonionic gadolinium HP-DO3A (ProHance) contrast agents have lower osmolality and greater stability, which make them superior compounds to gadolinium diethylenetriamine-pentacetic acid (Gd-DTPA). Therefore, the nonionic gadolinium contrasts have been safely administered more rapidly, in higher or multiple doses for contrast enhanced MRI without adverse side effects or changes in serum iron or total bilirubin, and the intensity of the area of enhancement and number of lesions detected were superior to that of Gd-DTPA (Magnevist) at the standard dose (0.1 mmol/Kg). Perhaps if the nonionic gadolinium contrast agent, ProHance, had been approved by the Food and Drug Administration (FDA) when this MRI was performed in 1990 it would have aided in providing contrast enhancement and visualization of the tumor lesion to assist in patient diagnosis and management. Magnetic resonance imaging also provides unique multiplanar capabilities that allow for optimal visualization of the temporal and occipital lobes of the brain without bone interference.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Neoplasms↗