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N Biswas

Publications and source records attributed to N Biswas.

At least 37 records · Page 2Linked to original sources
PubMed1997

Possible role of isoaspartyl methyltransferase towards regulation of acid trehalase activity in Saccharomyces cerevisiae.

Logarithmically growing cells of S. cerevisiae contained high neutral trehalase (NT) activity while stationary-phase cells had high acid trehalase (AT) activity. Change in activity profile of AT and NT were different during growth under different conditions, particularly during growth in acetate medium and up to 1 h of germination period, but that for AT and isoaspartyl methyltransferase (IMT) were found to be almost identical. Concomitant increase in NT activity as well as increase in cAMP level was noticed at the onset of spore germination. Increase in AT and IMT activities as well as decrease in S-adenosyl-L-methionine (AdoMet) level were noticed during stationary phase of growth. Acidic polyacrylamide gel electrophoresis and subsequent autoradiography revealed that substrate of IMT was a protein of molar mass around 82 kDa which could be an AT. Methylated AT was found to be more active while non-methylated AT was relatively less active in comparison to the untreated sample. Since AT existed as an equilibrium mixture of protomer and oligomer, it was suggested that IMT catalysed carboxyl methylation might have some contribution towards the regulation of AT activity.

Electrophoresis, Polyacrylamide Gel↗
PubMed1996

Characterisation of an acid trehalase of Saccharomyces cerevisiae present in trehalase-sucrase aggregate.

An acid trehalase-sucrase aggregate was purified (by 780-fold) from Saccharomyces cerevisiae, following conventional protein purification techniques, to an apparent yield of 18.5%. The aggregate was electrophoretically homogeneous but contained 175, 90, 68, 60, 40 molar mass (kDa) bands on SDS-electrophoresis. The purified aggregate had a specific activity (acid trehalase) of 22 U/mg; a Km value of 5.0 mM but contained 3-times more sucrase activity. Only sucrose and trehalose were hydrolysed by this aggregate and both activities were inhibited by acetate or phosphate. Temperature and pH optima for trehalose hydrolysis appeared to be 40-45 degrees C and 5.0, respectively. The purified aggregate appeared to be disaggregating spontaneously resulting in inactivation of both enzymes, which was enhanced either at pH 3.5 or at pH 7.0. Separation of acid trehalase from the aggregate by hydrophobic interaction chromatography resulted in inactivation. Rechromatography (HPGPLC) of the purified aggregate also gave disaggregation as well as inactivation of both enzymes. Disaggregated acid trehalase and sucrase contained 20-fold and 13-fold lower specific activities, respectively, and appeared to be unstable. Based on these observations we suggest that acid trehalase is stabilised by aggregation with sucrase.

Chromatography, High Pressure Liquid↗
PubMed1996

Optic disc in fundus coloboma.

PURPOSE: To categorize and describe the type of optic disc involvement and blood vessel patterns seen in patients with fundus coloboma. METHODS: This is a prospective study involving 67 eyes of 40 patients with choroidal coloboma. The evaluation included documentation of fundus details using fundus drawings or photographs, or both. RESULTS: Six types of disc involvement were identified: (1) normal disc outside fundus coloboma (27.8%); (2) disc outside the fundus coloboma and abnormal (10.4%); (3) disc outside the fundus coloboma and independently colobomatous (8.9%); (4) disc within the fundus coloboma and normal (5.0%); (5) disc within the fundus coloboma and colobomatous (44.3%); and (6) disc shape not identified but blood vessels seen emanating from the superior border of the large fundus coloboma (2.9%). Visual acuity was better in types I, II, and III compared with IV, V, and VI. Microphthalmos was more common with the more severe anomalies. High myopia was more common in the less severe anomalies. CONCLUSION: Optic disc involvement in fundus coloboma is widely variable. Of fundus colobomas, 67.2% are associated with either a frankly colobomatous or an altered disc. Of the discs located outside fundus colobomas, 41% are also abnormal. Visual acuity was better in types I, II, and III.

Adolescent↗