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Biomedical subjects

S K Saha

Publications and source records attributed to S K Saha.

At least 55 records · Page 3Linked to original sources
PubMed1998

A study of mycetoma in eastern India.

Forty consecutive cases of mycetoma were studied with respect to clinico-epidemiological, histopathological and radiological features. The age of the patients ranged from 17 to 57 years mean being 32.4 +/- 8.68. The disease was equally distributed amongst the sexes. Most of the patients had a rural background and the disease occurred mainly among farmers and housewives. Actinomycetes (32 cases. 80%) were found to be the main pathogenic organism and Eumycetes in 4 cases (20%) only. Clinical features were more or less the same irrespective of the aetiologic agent, consisting of local swelling with discharging sinuses. History of trauma was present in only 20% cases and 80% were incidental. Foot (28/40 i.e. 70%) was the commonest site of infection. Radiological bony involvement was detected in 14 out of 18 cases examined (38.88%). Out of the 32 radiographed patients of actinomyetoma 10(31.25%) showed bony involvement whereas all the four. Eumycetoma cases radiographed, had bony involvement. The notable bony changes were sclerosis, erosions, periosteal thickening and osteoporosis.

Actinomycetales Infections↗
PubMed1997

The increasing burden of disease in Bangladeshi children due to Haemophilus influenzae type b meningitis.

A laboratory-based study of diagnosed bacterial meningitis in the national paediatric hospital identified 852 cases of meningitis in the 8-year period 1987-1994. There were 587 culture-positive cases, of which Haemophilus influenzae (47%) and Streptococcus pneumoniae (32%) accounted for 80%. H. influenzae showed a remarkable increase of 700% during the study period. Most of the H. influenzae cases (90%) occurred in the 1st 2 years of life. Analysis of culture-negative specimens by antigen detection in the last 2 years also revealed the predominance of H. influenzae (71.4%) and S. pneumoniae (22.4%). Typing of H. influenzae isolates during this time showed that 98% of the strains were type b. This retrospective hospital-based study indicated a pronounced increase in the incidence of H. influenzae meningitis and strongly supports the need for large-scale Hib vaccination for young children. However, such nationwide intervention will probably need to be based on a prospective on a prospective and population-based surveillance of H. influenzae infections.

Age Distribution↗
PubMed1997

Serotypes of Streptococcus pneumoniae causing invasive childhood infections in Bangladesh, 1992 to 1995.

One hundred sixty-five invasive Streptococcus pneumoniae strains were isolated from children under five at Dhaka Shishu (Children's) Hospital during the period 1992 to 1995. Ninety-four strains were from cerebrospinal fluid, and 71 were from blood. More than 91% of the strains were isolated from patients aged 24 months or less. Predominant serotypes were, in descending order 7F, 12F, 14, 15B, 18, 5, and 22A. These comprised 70% of all isolates. The marked differences in serotype distribution in different countries indicate the need for a sentinel surveillance study for the countries of South Asia, particularly Bangladesh, China, India, and Pakistan.

Bacterial Vaccines↗
PubMed1997

Effects of nitric oxide synthase inhibition on phospholipid fatty acid composition of brown adipose tissue.

We investigated the effects of nitric oxide synthase inhibition on the phospholipid fatty acid composition of brown adipose tissue by administering chronic N omega-nitro-L-arginine methyl ester (L-NAME) (0.01%) to rats via drinking water. L-NAME caused a significant decrease in C14:0, C16:0, C16:1 and C18:1, with a concomitant increase in C18:0 and C18:2, L-NAME treatment elicited an increase in the unsaturation index. There were no significant changes in other fatty acids including the polyunsaturated fatty acids docosahexaenoate (DHA, C22:6) and arachidonate (C20:4). Polyunsaturated fatty acid linoleate (C18:2) was increased and the arachidonate index decreased in the L-NAME-treated group, suggesting a diminished conversion of C18:2 to C20:4.

Adipose Tissue↗
PubMed1996

Mechanistic interpretation of tryptophan fluorescence quenching in the time courses of glutamate dehydrogenase catalyzed reactions.

We have related the ratios of the protein fluorescence quenching and nucleotide absorbance time courses for the glutamate dehydrogenase catalyzed oxidative deamination of L-glutamate to identify the occurrence and sequential location of a previously demonstrated charge-transfer intermediate. Static studies showed the major portion of the fluorescence quenching signal to be due to radiationless singlet energy transfer from tryptophan to reduced coenzyme chromophores and that conformational changes contribute little to this signal. The ratio approach applied to the transient time courses shows correspondingly that, over most of the time range, the fluorescence quenching signal provides a quantitative measure of the sum of all posthydride transfer species. However, it also indicates the very early occurrence of a species of anomalous optical properties for the reaction catalyzed by the Clostridium symbiosum enzyme as well as that from bovine liver. Transient-state kinetic isotope effect time courses of both the fluorescence and the absorbance signals confirm that this species must be the prehydride charge-transfer complex in both enzyme reactions. Kinetic analysis of alpha-deuterio- and alpha-protio-L-glutamate reaction time courses proves the kinetic competence of the assignments. These results also demonstrate that the intramolecular transfer of a proton from the alpha-amino group of the substrate to an immediately adjacent aspartate carboxylate group on the enzyme is an obligatory initial event in the reactions catalyzed by both enzyme species, even though the occurrence of protein release from a critical lysine residue to the solvent occurs at different phases in those two reactions. The abnormally low intrinsic KIE required to simulate both the alpha-deuterio-L-glutamate reaction and its protio counterpart implies that the transition state of the hydride transfer step must be highly asymmetric.

Animals↗
PubMed1996

A difference in the sequence of steps in the reactions catalyzed by two closely homologous forms of glutamate dehydrogenase.

Glutamate dehydrogenase from beef liver (bl GDH) and the corresponding enzyme from Clostridium symbiosum (cs GDH) each catalyze the same sequence of chemical events in the oxidative deamination of L-glutamate. This catalysis involves interactions between at least six conserved functional groups, each of which appears to occupy the same geometric position with respect to the substrate molecule in both enzyme--coenzyme--L-glutamate reactive ternary complexes. In both cases steady-state V/K pH profiles indicate the requirement for the transfer to the solvent of a single proton from the same abnormal lysine for L-glutamate to bind and react; the pK of that lysine is the same for both enzymes. Here we report studies of the proton traffic between enzyme and solvent using direct pH-stat back-titration and indicator dye measurements on dead-end inhibitor ternary complexes, simultaneous transient-state time courses of proton and product, and transient-state kinetic isotope studies on both enzymes. We find that in the cs GDH catalyzed reaction the single proton is released only after the hydride transfer step whereas in the bl GDH reaction this proton release occurs prior to the hydride transfer step, despite the fact that the substrate molecule undergoes the same sequence of chemical events in both reactions. Interpreting these results in the context of the X-ray crystallographic structures of cs GDH and its NAD binary complex and of thermodynamic studies of bl GDH and its complexes, we conclude that the difference in the relative times of proton release in the two enzyme-catalyzed reactions must be ascribed to a difference in the sequence of active site cleft-opening and -closing events in the two identical reaction sequences. We suggest a possible biological significance to this unusual method of modulating a common reaction to suit differing metabolic roles.

Animals↗
PubMed1996

Interpretation of transient-state kinetic isotope effects.

In contrast to steady-state kinetic isotope effects (KIE's), transient-state KIE's are dependent on both time and signal source. We developed a theory which predicts the behavior of transient-state KIE's, permits the calculation of the intrinsic KIE, and makes possible the assignment of various optical signals to either pre- or post-hydride transfer events. We proved that the behavior of KIEobs for a reversible two-step reaction for all possible values of the rate constants and all possible ratios of intermediate and product contributions obeys three simple rules (assuming that the isotope-sensitive step involves a hydride transfer): (1) If only the post-hydride species contributes to the observed signal, KIEobs = KIEint at t = 0 and then decreases with time. (2) If only the pre-hydride species contributes to the observed signal, then KIEobs = 1 at t = 0 and then decreases with time. (3) If both pre- and post-hydride species contribute to the observed signal, then KIEobs = 1 at t = 0 and then will either rise or fall with time depending on the relative molar signal coefficients of the pre- and post-hydride species. We provide experimental evidence that the phenomena predicted by this theory do in fact occur in enzyme-catalyzed reactions.

Isotope Labeling↗
PubMed1996

Trypsin inhibitors from ridged gourd (Luffa acutangula Linn.) seeds: purification, properties, and amino acid sequences.

Two trypsin inhibitors, LA-1 and LA-2, have been isolated from ridged gourd (Luffa acutangula Linn.) seeds and purified to homogeneity by gel filtration followed by ion-exchange chromatography. The isoelectric point is at pH 4.55 for LA-1 and at pH 5.85 for LA-2. The Stokes radius of each inhibitor is 11.4 A. The fluorescence emission spectrum of each inhibitor is similar to that of the free tyrosine. The biomolecular rate constant of acrylamide quenching is 1.0 x 10(9) M-1 sec-1 for LA-1 and 0.8 x 10(9) M-1 sec-1 for LA-2 and that of K2HPO4 quenching is 1.6 x 10(11) M-1 sec-1 for LA-1 and 1.2 x 10(11) M-1 sec-1 for LA-2. Analysis of the circular dichroic spectra yields 40% alpha-helix and 60% beta-turn for La-1 and 45% alpha-helix and 55% beta-turn for LA-2. Inhibitors LA-1 and LA-2 consist of 28 and 29 amino acid residues, respectively. They lack threonine, alanine, valine, and tryptophan. Both inhibitors strongly inhibit trypsin by forming enzyme-inhibitor complexes at a molar ratio of unity. A chemical modification study suggests the involvement of arginine of LA-1 and lysine of LA-2 in their reactive sites. The inhibitors are very similar in their amino acid sequences, and show sequence homology with other squash family inhibitors.

Amino Acid Sequence↗
PubMed1996

Efficacy of metronidazole lavage in treatment of intraperitoneal sepsis. A prospective study.

In a prospective study, 182 consecutive patients were included for the treatment of intraabdominal sepsis with adjuvant metronidazole lavage that was carried out at the end of the operative procedures. Eighty of them underwent emergency surgery for peritonitis and 102 elective surgery for a variety of lesions. Although fecal peritonitis was found in 23 and malignant tumors in 84 patients, there was not a single instance of intraabdominal abscess in 182 patients, but the incidence of wound infection was 2.66% in the emergency group and 0% in the elective group; mortality was 5% and 3.9%, respectively. Therefore, adjuvant metronidazole lavage provides confidence in the treatment of intraperitoneal abscess, and it enhances a quick recovery. It is safe to use and cost effective.

Abdominal Abscess↗
PubMed1996

Interpretation of the Widal test in the diagnosis of typhoid fever in Bangladeshi children.

The value of a Widal test in diagnosing typhoid fever was assessed in children aged between 1 and 10 years in Bangladesh. The test was done on sera specimens from 300 healthy school children, 100 patients with non-typhoidal febrile illness and 150 bacteriologically proven cases of typhoid fever. Salmonella typhi O and H agglutinin titres > 1:80 and > 1:160 were considered to be significant with 88% sensitivity and 98% specificity, respectively. Among the bacteriologically proven cases, 11.3% showed no response to either agglutinin, and in another 17.3% of cases there was no response for TO agglutinin. This study suggests that in children in an endemic area a positive Widal test is of considerable importance in diagnosing typhoid fever. Furthermore, negative results should be interpreted with caution and both the agglutinins must be considered equally important. Reliance on somatic (TO) antigen only will result in missed diagnosis.

Agglutination Tests↗
PubMed1996

Molecular typing of Salmonella typhi strains from Dhaka (Bangladesh) and development of DNA probes identifying plasmid-encoded multidrug-resistant isolates.

Seventy-eight Salmonella typhi strains isolated in 1994 and 1995 from patients living in Dhaka, Bangladesh, were subjected to phage typing, ribotyping, IS200 fingerprinting, and PCR fingerprinting. The collection displayed a high degree of genetic homogeneity, because restricted numbers of phage types and DNA fingerprints were observed. A significant number of the S. typhi strains (67%) were demonstrated to be multiple drug resistant (MDR). The vast majority of the MDR strains were resistant to chloramphenicol, ampicillin, trimethoprim, streptomycin, sulfamethoxazole, and tetracycline (R type CATmSSuT), a resistance phenotype that has also frequently been observed in India. Only two strains displayed a distinct MDR phenotype, R type AT-mSSuT. Pulsed-field gel electrophoresis demonstrated the presence of large plasmids exclusively in the MDR strains of both R types. The plasmids present in the S. typhi strains of R type CATmSSuT could be conjugated to Escherichia coli and resulted in the complete transfer of the MDR phenotype. PCR fingerprinting allowed discrimination of MDR and susceptible strains. The DNA fragments enabling discrimination of MDR and susceptible S. typhi strains by PCR were useful genetic markers for identifying MDR encoded by large plasmids of the H1 incompatibility group.

Bacterial Typing Techniques↗
PubMed1996

A regulatory mechanism for the balanced synthesis of membrane phospholipid species in Escherichia coli.

The mechanism that assures the balanced synthesis of zwitterionic (phosphatidylethanolamine) and acidic phospholipids (phosphatidylglycerol and cardiolipin) in Escherichia coli has been examined by genetically manipulating the two enzymes at the biosynthetic branch point, i.e., phosphatidylglycerophosphate synthase, encoded by pgsA, and phosphatidylserine synthase, encoded by pssA. A mutant in which the most part of the pssA gene was replaced with a drug resistance gene lacked phosphatidylserine synthase and phosphatidylethanolamine and required divalent metal ions for growth, as did a previously reported insertion-inactivated pssA mutant. When this mutant harbored a plasmid containing a Bacillus subtilis gene that encodes membrane-bound phosphatidylserine synthase, the phosphatidylethanolamine content was dependent on its activity, in contrast to that with the soluble E. coli counterpart. A defective mutation, pgsA3, caused reductions not only in acidic-phospholipid synthesis but also in phosphatidylethanolamine synthesis, despite the normal level of phosphatidylserine synthase activity. These results, together with previous observations, indicate that phosphatidylserine synthesis requires the membrane-associated form of phosphatidylserine synthase, which is related to the membrane-levels of acidic phospholipids, thus yielding balanced compositions of zwitterionic and acidic phospholipids.

Bacillus subtilis↗
PubMed1996

Directed mutagenesis, Ser-56 to Pro, of Bacillus subtilis phosphatidylserine synthase drastically lowers enzymatic activity and relieves amplification toxicity in Escherichia coli.

Amino acid residue 56 of the phosphatidylserine synthase of Bacillus subtilis was changed from Ser to Pro by using modified primers in PCR amplification of its structural gene, pssBS. When an Escherichia coli mutant lacking its own phosphatidylserine synthase harbored a plasmid carrying this allele, the Mn(2+)-requiring Bacillus-type synthase activity, as assayed in vitro, was at least six-fold lower than that with the wild-type pssBS gene and the cellular phosphatidylethanolamine content was similarly lowered, indicating that the altered region of the enzyme is critically important for its activity. In contrast to the E. coli counterpart, amplification of the wild-type Bacillus enzyme increased both the relative and absolute contents of phosphatidylethanolamine and impaired cell growth. However, amplification of the mutant enzyme of the same level was much less toxic, implying that E. coli cells are more sensitive to the unbalanced accumulation of phosphatidylethanolamine than that of the hydrophobic enzyme molecules. Possible roles of the conserved region of the enzyme in its activity and the wild-type phospholipid composition in the proper membrane function are discussed.

Alleles↗
PubMed1996

Effects of acute and chronic inhibition of nitric oxide synthase on brown adipose tissue thermogenesis.

This study was undertaken to examine the possible role of nitric oxide (NO) on brown adipose tissue (BAT) thermogenesis in rats. The chronic administration of N omega-nitro-L-arginine methyl ester (L-NAME; NO synthase inhibitor) in drinking water given to rats decreased interscapular BAT (IBAT) weight as well as DNA content in a warm environment (25 +/- 1 degrees C; 2 and 4 weeks), and inhibited the cold-stimulated (5 +/- 1 degrees C; 2 weeks) increase in IBAT weight and DNA content. L-Arginine administration (4 weeks in a warm environment) increased the DNA content of IBAT. Chronic L-NAME administration (2 weeks in a warm environment) eliminated the NE-stimulated increase in in vivo oxygen consumption (VO2), caused hypothermia in acute cold exposure (0 degree C), and suppressed the NE-stimulated increase in in vitro IBAT VO2. In vitro incubation of native IBAT with L-NAME suppressed the basal and NE-stimulated increase in in vitro VO2. In vitro incubation of IBAT with methylene blue (soluble guanylate cyclase inhibitor and a scavenger of free NO) eliminated the NE-stimulated increase in in vitro IBAT VO2. These results suggest that the nitric oxide and NO-cGMP signaling systems are involved in the regulation of BAT cellularity and thermogenesis in rats.

Adipose Tissue, Brown↗
PubMed1994

The demonstration of a glutamate dehydrogenase-NADP-L-glutamate charge-transfer complex and its location on the reaction pathway.

In previous transient state kinetic work from this laboratory, we proposed a new mechanism for the glutamate dehydrogenase-catalyzed oxidative deamination reaction involving an initial replacement of a proton from lysine 126 by a single bound water molecule, followed by closure of the active site cleft and expulsion of bulk water, providing a hydrophobic environment for the ensuing hydride transfer step. Here, we report the results of further transient state fluorescence, absorbance, and kinetic isotope effect studies, which demonstrate the occurrence of an unusual intermediate in the early steps of that reaction. This phenomenon is revealed by an initial fluorescence burst that occurs in the time period where the absorbance signal is still in its lag phase. Using an extension of the proton/product ratio approach we have described earlier, we show that this intermediate is a strongly fluorescent but weakly absorbing species whose absorption maximum is red-shifted beyond that of other known complexes of this enzyme. The transient state kinetic isotope effects of the fluorescence and absorbance signals are compatible only with a reaction scheme in which the formation of the fluorescent complex precedes the hydride transfer step. The optical properties of this enzyme-oxidized coenzyme-substrate intermediate strongly suggest that it is a charge-transfer complex, similar in nature to the complex responsible for the well known "Racker band" reported in 1952 for glyceraldehyde-3-phosphatase dehydrogenase (Racker, E., and Krimsky, I. (1952) Nature 169, 1043-1044). The crystal structure studies of the enzyme-coenzyme and enzyme-L-glutamate complexes of the closely analogous Clostridium symbosium glutamate dehydrogenase, reported by the Sheffield group (Stillman, T. J., Baker, P. J., Britton, K. L., and Rice, D. W. (1993) J. Mol. Biol. 234, 1131-1139), provide a basis for a physical explanation of the phenomenon. We conclude that the charge transfer phenomenon is caused by the near apposition of the unprotonated alpha-amino group of the substrate in a form of the enzyme in which a conformational change has caused the complete closing of the active site cleft.

Animals↗