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Biomedical subjects

M A Bhat

Publications and source records attributed to M A Bhat.

26 records · Page 2Linked to original sources
PubMed1998

Neurexin IV, caspr and paranodin--novel members of the neurexin family: encounters of axons and glia.

Axonal insulation is of key importance for the proper propagation of action potentials. In Drosophila and other invertebrates, it has recently been demonstrated that septate junctions play an essential role in axonal insulation or blood-brain-barrier formation. Neurexin IV, a molecular component of Drosophila septate junctions, has been shown to be essential for axonal insulation in the PNS in embryos and larvae. Interestingly, a vertebrate homolog of Neurexin IV, caspr--also named paranodin--has been shown to localize to septate-like junctional structures. These vertebrate junctions are localized to the paranodal region of the nodes of Ranvier, between axons and Schwann cells. Caspr/paranodin might play an important role in barrier formation, and link neuronal membrane components with the axonal cytoskeletal network.

Action Potentials↗
PubMed1996

A Drosophila neurexin is required for septate junction and blood-nerve barrier formation and function.

Septate and tight junctions are thought to seal neighboring cells together and to function as barriers between epithelial cells. We have characterized a novel member of the neurexin family, Neurexin IV (NRX), which is localized to septate junctions (SJs) of epithelial and glial cells. NRX is a transmembrane protein with a cytoplasmic domain homologous to glycophorin C, a protein required for anchoring protein 4.1 in the red blood cell. Absence of NRX results in mislocalization of Coracle, a Drosophila protein 4.1 homolog, at SJs and causes dorsal closure defects similar to those observed in coracle mutants. nrx mutant embryos are paralyzed, and electrophysiological studies indicate that the lack of NRX in glial-glial SJs causes a breakdown of the blood-brain barrier. Electron microscopy demonstrates that nrx mutants lack the ladder-like intercellular septa characteristic of pleated SJs (pSJs). These studies identify NRX as the first transmembrane protein of SJ and demonstrate a requirement for NRX in the formation of septate-junction septa and intercellular barriers.

Amino Acid Sequence↗
PubMed1996

Chromatid segregation at anaphase requires the barren product, a novel chromosome-associated protein that interacts with Topoisomerase II.

We have isolated a Drosophila gene, barren (barr), required for sister-chromatid segregation in mitosis. barr encodes a novel protein that is present in proliferating cells and has homologs in yeast and human. Mitotic defects in barr embryos become apparent during cycle 16, resulting in a loss of PNS and CNS neurons. Centromeres move apart at the metaphase-anaphase transition and Cyclin B is degraded, but sister chromatids remain connected, resulting in chromatin bridging. This phenotype is similar to that described in TOP2 mutants in yeast. Barren protein localizes to chromatin throughout mitosis. Colocalization and biochemical experiments indicate that Barren associates with Topoisomerase II throughout mitosis and alters the activity of Topoisomerase II. We propose that this association is required for proper chromosomal segregation by facilitating the decatenation of chromatids at anaphase.

Anaphase↗
PubMed1994

Identification and characterization of a new plasmid carrying genes for degradation of 2,4-dichlorophenoxyacetate from Pseudomonas cepacia CSV90.

Pseudomonas cepacia CSV90 is able to utilize 2,4-dichlorophenoxyacetate (2,4-D) and 2-methyl-4-chlorophenoxyacetate as sole sources of carbon and energy. Mutants of the strain CSV90 which had lost this ability appeared spontaneously on a nonselective medium. The wild-type strain harbored a 90-kb plasmid, pMAB1, whereas 2,4-D-negative mutants either lost the plasmid or had a 70-kb plasmid, pMAB2. The plasmid pMAB2 was found to have undergone a deletion of a 20-kb fragment of pMAB1. The plasmid-free mutants regained the ability to degrade 2,4-D after introduction of purified pMAB1 by electroporation. Cloning in Escherichia coli of a 10-kb BamHI fragment from pMAB1, the region absent in pMAB2, resulted in the expression of the gene tfdC encoding 3,5-dichlorocatechol 1,2-dioxygenase. After subcloning, the tfdC gene was located in a 1.6-kb HindIII fragment. The nucleotide sequence of the tfdC gene and the restriction map of its contiguous region are identical to those of the well-characterized 2,4-D-degradative plasmid pJP4 of Alcaligenes eutrophus, whereas the overall restriction maps of the two plasmids are different. The N-terminal 44-amino-acid sequence of the enzyme purified from the strain CSV90 confirmed the reading frame in the DNA sequence for tfdC and indicated that the initiation codon GUG is read as methionine instead of valine.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1993

Purification of 3,5-dichlorocatechol 1,2-dioxygenase, a nonheme iron dioxygenase and a key enzyme in the biodegradation of a herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), from Pseudomonas cepacia CSV90.

An enzyme which cleaves the benzene ring of 3,5-dichlorocatechol has been purified to homogeneity from Pseudomonas cepacia CSV90, grown with 2,4-dichlorophenoxyacetic acid (2,4-D) as the sole carbon source. The enzyme was a nonheme ferric dioxygenase and catalyzed the intradiol cleavage of all the examined catechol derivatives, 3,5-dichlorocatechol having the highest specificity constant of 7.3 microM-1s-1 in an air-saturated buffer. No extradiol-cleaving activity was observed. Thus, the enzyme was designated as 3,5-dichlorocatechol 1,2-dioxygenase. The molecular weight of the native enzyme was ascertained to be 56,000 by light scattering method, while the M(r) value of the enzyme denatured with 6 M guanidine-HCl or sodium dodecyl sulfate was 29,000 or 31,600, respectively, suggesting that the enzyme was a homodimer. The iron content was estimated to be 0.89 mol per mole of enzyme. The enzyme was deep red and exhibited a broad absorption spectrum with a maximum at around 425 nm, which was bleached by sodium dithionite, and shifted to 515 nm upon anaerobic 3,5-dichlorocatechol binding. The catalytic constant and the Km values for 3,5-dichlorocatechol and oxygen were 34.7 s-1 and 4.4 and 652 microM, respectively, at pH 8 and 25 degrees C. Some heavy metal ions, chelating agents and sulfhydryl reagents inhibited the activity. The NH2-terminal sequence was determined up to 44 amino acid residues and compared with those of the other catechol dioxygenases previously reported.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1991

Affinity purification and characterization of 2,4-dichlorophenol hydroxylase from Pseudomonas cepacia.

2,4-Dichlorophenol hydroxylase, a flavoprotein monooxygenase from Pseudomonas cepacia grown on 2,4-dichlorophenoxyacetic acid (2,4-D) as the sole source of carbon, was purified to homogeneity by a single-step affinity chromatography on 2,4-DCP-Sepharose CL-4B. The enzyme was eluted from the affinity matrix with the substrate 2,4-dichlorophenol. The enzyme has a molecular weight of 275,000 consisting of four identical subunits of molecular weight 69,000 and requires exogenous addition of FAD for its complete catalytic activity. The enzyme required an external electron donor NADPH for hydroxylation of 2,4-dichlorophenol to 3,5-dichlorocatechol. NADPH was preferred over NADH. The enzyme had Km value of 14 microM for 2,4-dichlorophenol, and 100 microM for NADPH. The enzyme activity was significantly inhibited by heavy metal ions like Hg2+ and Zn2+ and showed marked inhibition with thiol reagents. Trichlorophenols inhibited the enzyme competitively. The hydroxylase activity decreased as a function of increasing concentrations of Cibacron blue and Procion red dyes. The apoenzyme prepared showed complete loss of FAD when monitored spectrophotometrically and had no enzymatic activity. The inactive apoenzyme was reconstituted with exogenous FAD which completely restored the enzyme activity.

Apoenzymes↗
PubMed1991

A double-blind randomized cross-over comparison of high-dose prochlorperazine with high-dose metoclopramide for cisplatin-induced emesis.

This double-blind randomized cross-over study was conducted to compare the safety and efficacy of high-dose prochlorperazine infusion and dexamethasone (HDPD) with an effective and safe combination of high-dose metoclopramide and dexamethasone (HDMD) in controlling cisplatin-induced emesis. None of the patients entering the study had received any prior chemotherapy. High-dose cisplatin was administered on an inpatient basis. Twenty eligible patients were analyzed based on the assessment made 24 h after the chemotherapy. The parameters compared were severity and duration of nausea and vomiting, severity of retching and side effects. Significantly less vomiting and retching episodes were recorded with HDPD combination. The severity of nausea was also less with this combination. There was no significant difference in the incidence of side effects.

Adult↗