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Biomedical subjects

R Nagarajan

Publications and source records attributed to R Nagarajan.

At least 73 records · Page 4Linked to original sources
PubMed1978

A32390A, a new biologically active metabolite. II. Isolation and structure.

An inhibitor of dopamine-beta-hydroxylase, designated A32390A, was isolated from the culture broth of a Pyrenochaeta species. The inhibitor showed antimicrobial activity against fungi and gram-positive bacteria. Spectroscopic analysis and chemical degradation studies indicated that the structure was 1,6-di-O-(2-isocyano-3-methylcrotonyl)-D-mannitol.

Animals↗
PubMed1974

Synthesis of deactoxycephalosporin C by a mutant of Cephalosporium acremonium.

A number of Cephalosporium acremonium mutants blocked in the synthesis of cephalosporin C were investigated for accumulation of other beta-lactam compounds. The non-cephalosporin C producers were isolated after exposing the superior cephalosporin C-producing strain M8650-4 to ultraviolet light (268 nm). One of the blocked mutants, MH63, accumulated deacetylcephalosporin C (0.4 mg/ml), deacetoxycephalosporin C (1.5 mg/ml), and penicillin N (2.7 mg/ml). In contrast, the parent of MH63 produced high levels of cephalosporin C as well as deacetylcephalosporin C (2.2 mg/ml) and penicillin N (1.0 mg/ml), but only traces of deacetoxycephalosporin C (about 0.1 mg/ml). Deacetoxycephalosporin C was isolated from the mutant strain and identified by ultraviolet light, nuclear magnetic resonance, bioactivity spectrum, and co-migration with authentic standard in three chromatography systems.

Acremonium↗
PubMed1972

Origin of glycine from acid hydrolysis of the -lactam antibiotic A16886B.

Structural analysis of two new beta-lactam antibiotics, A16884A and A16886B, indicated that they, like cephalosporin C, were composed of modified valine and cysteine residues, and alpha-aminoadipic acid. However, acid hydrolysis of A16886B and A16884A produced three times as much glycine as did hydrolysis of cephalosporin C under the same conditions. Samples of A16886B-(14)C-6 and A16886B-(14)C-8 were prepared by the addition of cysteine-(14)C-3 and cystine-(14)C-1 to fermentations of Streptomyces clavuligerus. The specific activity of glycine obtained from hydrolysis of A16886B-(14)C-6 was considerably higher than that from hydrolysis of A16886B-(14)C-8. An explanation for the difference in amounts of glycine obtained from hydrolysis of these antibiotics is discussed.

Carbamates↗
PubMedDate not supplied

Block copolymer microdomains: a novel medium for enzymatic reactions.

Block copolymers exhibit the phenomenon of microdomain formation in pure states as well as in solutions. The microdomains vest the block copolymer assemblies with the intriguing characteristics of microheterogeneous media. We demonstrate that this microheterogeneity in hydrophobic-hydrophilic block copolymer systems can be exploited for immobilizing enzymes and to carry out enzymatic reactions. Examples involving cholesterol oxidase and horseradish peroxidase are provided here. The observed changes in the enzymatic activity in block copolymer microdomains from that in the aqueous media are interpreted in terms of the hydrophobicity of the reaction microenvironment. The block copolymer microdomains are simple to generate, well defined, and easily reproducible. Therefore, they hold significant potential as media for enzymatic biosynthetic reactions when the substrates or the reaction products are water insoluble.

Benzocycloheptenes↗
PubMedDate not supplied

Release and recovery of porcine pepsin and bovine chymosin from reverse micelles: a new technique based on isopropyl alcohol addition.

After complete solubilization by the direct method, porcine pepsin was not released from AOT in isooctane reverse micelles even under aqueous-phase conditions which would not ordinarily allow uptake. Similarly, bovine chymosin, once forward-transferred at a pH below its isoelectric point, was not back-transferred into an aqueous contact phase buffered at a pH value above its isoelectric point. These results show that there is significant hysteresis in the forward- and backward-transfer processes and further imply that kinetics, and not equilibrium, control uptake or release processes for these enzymes. The addition of 10-15% isopropyl alcohol to the aqueous phase increases the rate of protein release dramatically and allows for nearly complete back-transfer of porcine pepsin and 70% back-transfer of bovine chymosin. IPA addition does not destroy the functional integrity of the system since forward transfer of bovine chymosin still occurs at pH values below (but not above) the pI of the protein.

1-Propanol↗
PubMedDate not supplied

Transcatheter closure of perimembranous ventricular septal defect with amplatzer membranous occluder.

BACKGROUND: Use of trancatheter device closure for membranous ventricular septal defect is still in evolving phase. We report the early and mid-term results of our experience with the new asymmetric Amplatzer membranous ventricular septal defect occluder. METHODS AND RESULTS: We attempted, transcatheter closure of perimembranous ventricular septal defect using asymmetric Amplatzer occluder in 26 patients. The patients were selected on the basis of transthoracic and transesophageal echocardiographic assessment of the ventricular septal defect. The procedure was successful in 21 (81%) patients. The age ranged from 3 to 23 years, weight from 10 to 59 kg and defect size ranged from 3 to 9 mm (mean: 5 +/- 1.8 mm). One patient had situs inversus with dextrocardia: 11 had aneurysmal tissue partly occluding the defect and the device was deployed either across (n=6) or within the aneurysmal sac (n=5). Three patients developed high degree atrioventricular block on attempts to cross the defect with the sheath and the procedure was discontinued. In two patients it was not possible to place the sheath in left ventricle despite repeated attempts. There was a residual flow in 4 (19%) patients at 24 hours. Two patients developed bundle branch block and none had complete heart block. At follow-up (1-9 months, n=20), residual flow was seen in two patients. None developed late conduction defect, aortic regurgitation, infective endocarditis or hemolysis. CONCLUSIONS: Transcatheter closure of perimembranous ventricular septal defect can be performed safely and effectively with the new asymmetric Amplatzer occluder device in selected patients with good short- and midterm results. These devices can be deployed safely in and across and the aneurysmal sacs. In selected cases, this procedure is a satisfactory alternative to surgery.

Adolescent↗