Search PubMed⌕ Search

Biomedical subjects

S Sarkar

Publications and source records attributed to S Sarkar.

At least 199 records · Page 11Linked to original sources
PubMed1995

Activation of the Aspergillus PacC transcription factor in response to alkaline ambient pH requires proteolysis of the carboxy-terminal moiety.

Extremes of pH are an occupational hazard for many microorganisms. In addition to efficient pH homeostasis, survival effectively requires a regulatory system tailoring the syntheses of molecules functioning beyond the cell boundaries (permeases, secreted enzymes, and exported metabolites) to the pH of the growth environment. Our previous work established that the zinc finger PacC transcription factor mediates such pH regulation in the fungus Aspergillus nidulans in response to a signal provided by the products of the six pal genes at alkaline ambient pH. In the presence of this signal, PacC becomes functional, activating transcription of genes expressed at alkaline pH and preventing transcription of genes expressed at acidic pH. Here we detect two forms of PacC in extracts, both forming specific retardation complexes with a PacC-binding site. Under acidic growth conditions or in acidity-mimicking pal mutants (defective in ambient pH signal transduction), the full-length form of PacC predominates. Under alkaline growth conditions or in alkalinity-mimicking pacCc mutants (independent of the ambient pH signal), a proteolysed version containing the amino-terminal approximately 40% of the protein predominates. This specifically cleaved shorter version is clearly functional, both as an activator for alkaline-expressed genes and as a repressor for acid-expressed genes, but the full-length form of PacC must be inactive. Thus, PacC proteolysis is an essential and pH-sensitive step in the regulation of gene expression by ambient pH. Carboxy-terminal truncations, resulting in a gain-of-function (pacCc) phenotype, bypass the requirement for the pal signal transduction pathway for conversion of the full-length to the proteolyzed functional form.

Aspergillus nidulans↗
PubMed1995

Overproduction and rapid purification of human fast skeletal beta troponin T using Escherichia coli expression vectors: functional differences between the alpha and beta isoforms.

Troponin T (TpnT), an essential component of the Ca(2+)-regulatory troponin complex, is involved in protein-protein interactions with other thin-filament proteins during muscle contraction in vertebrate striated muscle (VSM). The isoforms of TpnT are encoded by members of a multigene family which, by alternate splicing, produces a complex pattern of isoproteins in VSM. The functional domains of TpnT are only tentatively identified and structure-function analysis on this protein is limited due to the heterogeneity of the multiple isoforms. We reasoned that the overproduction and purification of a single TpnT species in Escherichia coli would provide an insight into these studies, besides being useful in crystallizing the protein. We cloned the human fast skeletal beta TpnT-encoding cDNA (beta TpnTf) in three expression vectors. Overexpression was achieved in an E. coli BL21 (DE3) lysogen using a T7 RNA polymerase promoter-based vector, pET17b. The unfused recombinant protein was purified by a simple and rapid procedure in a biologically active and immunoreactive form. This is the first successful synthesis of a complete beta TpnTf polypeptide from any species using an in vitro expression system. Purified human beta TpnTf, a predominant fetal form, was less Ca(2+)-sensitive and exhibited considerably reduced affinity for troponin C and tropomyosin, as compared to the rabbit fast skeletal alpha TpnT, a predominant adult isoform. These results provide a biochemical correlate to the age-related differences in Ca2+ sensitivity of tension development in vertebrate fast skeletal muscles.

Base Sequence↗
PubMed1995

The Aspergillus PacC zinc finger transcription factor mediates regulation of both acid- and alkaline-expressed genes by ambient pH.

The pH regulation of gene expression in Aspergillus nidulans is mediated by pacC, whose 678 residue-derived protein contains three putative Cys2His2 zinc fingers. Ten pacCc mutations mimicking growth at alkaline pH remove between 100 and 214 C-terminal residues, including a highly acidic region containing an acidic glutamine repeat. Nine pacC+/- mutations mimicking acidic growth conditions remove between 299 and 505 C-terminal residues. Deletion of the entire pacC coding region mimics acidity but leads additionally to poor growth and conidiation. A PacC fusion protein binds DNA with the core consensus GCCARG. At alkaline ambient pH, PacC activates transcription of alkaline-expressed genes (including pacC itself) and represses transcription of acid-expressed genes. pacCc mutations obviate the need for pH signal transduction.

Acid-Base Equilibrium↗
PubMed1995

The Indian experience with immediate tracheoesophageal puncture for voice restoration.

A 3-year prospective study on primary tracheoesophageal puncture was carried out at Nanavati Hospital and Tata Memorial Hospital, Bombay, to assess its feasibility in a developing country and its success in vocal rehabilitation. We report our experience with primary tracheoesophageal puncture in 64 patients (57 males and 7 females) following surgical treatment for carcinoma of the pyriform fossa (45 cases) and endolarynx (19 cases). All patients underwent total laryngectomies with or without partial pharyngectomy and primary pharyngeal mucosal closure. Fifty-one patients underwent primary surgery followed by postoperative radiotherapy. At 3 months successful tracheoesophageal speech was achieved in 84% patients, although this percentage decreased to 67% at 9 months. There were no major complications. Successful vocal rehabilitation was related more to "patient factors" such as delays in seeking medical attention when prosthetic valves dislodged, improper use and care of the valves and inability to learn speech with the prosthesis. Overall, primary tracheoesophageal puncture was found to be feasible and should be used more extensively for vocal rehabilitation following laryngectomy in developing countries.

Adult↗
PubMed1995

Influence of subclinical nematodosis on the kinetic disposition of fenbendazole in buffaloes.

The disposition kinetics of fenbendazole was studied in buffaloes subclinically infected with gastrointestinal nematodes. There was significantly reduced uptake of the drug in infected animals compared to uninfected controls. The pH of the duodenal liquor was highly alkaline compared to the acidic pH in uninfected animals. The egg count in the faeces never became zero though the numbers were reduced to a great extent compared to pre-treatment values. The influence of the host's physiology on the reduced bioavailability of fenbendazole is discussed.

Ancylostomatoidea↗
PubMed1995

Cadmium-induced lipid peroxidation and the status of the antioxidant system in rat tissues.

Cadmium may induce oxidative damage in different tissues by enhancing peroxidation of membrane lipids and altering the antioxidant system of the cells. The peroxidative damage to the cell membrane may cause injury to cellular components due to the interaction of metal ions with the cell organelles. The treatment with Cd (0.4 mg/kg body wt, ip) significantly increased lipid peroxidation (LPO) in heart within 3 h of the Cd injection, while the increase in kidney and liver followed 6 to 12 h after Cd intoxication. The antioxidant enzymes and other antioxidants provide protection to the cells against oxidative damage. The superoxide dismutase (SOD) activity increased in heart, kidney and liver within 24 h of Cd intoxication. The CAT activity increased significantly in heart 9 h after Cd injection; however, no significant change in CAT activity was observed in kidney and liver tissues. The GSH content and the activity of GR decreased in heart, kidney and liver 72 h after Cd administration, which has been suggested to be the cause for increased LPO in the tissues. The hexose monophosphate (HMP) shunt enzymes generate NADPH required for the activity of GR which may affect the GSH content in the tissues. The generalised decrease in glucose 6-phosphate dehydrogenase (G6PDH) and 6 phospho gluconate dehydrogenase (6PGDH) at 9 h followed by an increase in these enzymes in tissues 72 h after Cd intoxication suggest that the production of NADPH by the HMP shunt is required to reduce the oxidative damage. The results show that Cd induced LPO in the tissues and the condition was partially counteracted by the antioxidant system.

Animals↗
PubMed1995

Fatal injuries in motorcycle riders according to helmet use.

OBJECTIVE: Helmets have been shown to be effective in preventing head injuries in motorcyclists, but some studies have suggested that helmets may cause injury to parts of the head or neck because they add mass to the head. DESIGN: This study examined patterns of fatal injuries in helmeted and unhelmeted motorcyclists. MATERIALS AND METHODS: Coroner reports, hospital records, and police reports for motorcyclists fatally injured in crashes from July 1, 1988 through October 31, 1989 were examined. All injury diagnoses were abstracted and coded to the 1990 version of The Abbreviated Injury Scale and the International Classification of Diseases, 9th revision. MAIN RESULTS: Cerebral injury, intracranial hemorrhage, face, skull vault, and cervical spine injuries were more likely to be found in fatally injured unhelmeted motorcyclists than in helmeted motorcyclists. CONCLUSIONS: These results expand earlier reports showing that helmets provide protection for all types and locations of head injuries, and show that they are not associated with increased neck injury occurrence.

Abdominal Injuries↗