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Biomedical subjects

A M Mehta

Publications and source records attributed to A M Mehta.

15 recordsLinked to original sources
PubMed1991

Translational modification of an 18 kilodalton polypeptide by spermidine in rice cell suspension cultures.

When rice (Oryza sativa) cell suspension cultures are grown in the presence of [terminal methylenes-(3)H]spermidine, label is incorporated in a single polypeptide with a molecular mass of 18 kilodaltons on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Preincubation of cell cultures with polyamine biosynthesis inhibitors difluoromethylarginine and difluoromethylornithine, resulted in increased incorporation of the label into the 18 kilodalton polypeptide. In cells in which protein synthesis was arrested by cycloheximide, no label was detected in the 18 kilodalton polypeptide, suggesting a requirement for de novo protein synthesis.

Journal Article↗
PubMed1990

A novel metabolic form of the 32 kDa-D1 protein in the grana-localized reaction center of photosystem II.

Two forms of the 32 kDa-D1 reaction center protein of photosystem II (PSII), having slightly different mobilities on denaturing polyacrylamide gels, have been resolved in Spirodela oligorrhiza, Glycine max L., Gossypium hirsutum L., Triticum aestivum L., and Zea mays L. The protein band with faster mobility is identified as the 32 kDa-D1 protein, and the less mobile band as a novel form, designated 32*. The two forms are structurally similar based on immunological and partial proteolytic tests. 32* is associated exclusively with the grana and is present in the PSII reaction center. Temporally, 32* appears several hours after the translocation of newly synthesized and processed 32 kDa-D1 protein from the stroma lamellae to the grana. Formation of the 32* is strictly light-dependent under physiological light intensities and correlates with a reciprocal loss of the 32-kDa form. Light induced formation of 32* is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea but is not coupled to linear electron transport.

2,4-Dinitrophenol↗
PubMed1988

Identification of a unique isoform of 1-aminocyclopropane-1-carboxylic acid synthase by monoclonal antibody.

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase (EC 4.4.1.14) is a key enzyme regulating ethylene biosynthesis in higher plants. A monoclonal antibody (mAb T20C) that immunoprecipitates the ACC synthase activity from tomato pericarp tissue extracts revealed that mAb T20C immunodecorates an approximately 67-kDa polypeptide. On isoelectric focusing gels, ACC synthase activity in cell-free preparations was resolved into three distinct activity peaks with pI values 5.3, 7, and 9. mAb T20C specifically recognized the pI 7 form of the enzyme on electrophoretic transfer (Western) blots. When analyzed by sodium dodecyl sulfate gel electrophoresis under reducing conditions, the eluted pI 7 form was confirmed to migrate as a polypeptide of 67 kDa. The 67-kDa pI 7 isoform is a previously undescribed form of ACC synthase.

Journal Article↗
PubMed1984

Cooperative interactions in the system ribosomes-ribosomal protein S1-polynucleotide triplets.

Association equilibria have been determined in the ternary system uridyl triplets (T)-ribosomal protein S1 (S)-ribosomes (Rb) depleted of S1 at 6 and 10 mM Mg2+. For 1:1 stoichiometry of reactants, four thermodynamically independent equilibria characterize the ternary system. The binary interaction Rb + T was studied by following the fluorescence quenching of labeled ribosomes by added T. The Rb + T association constant for UpUpUp triplets was 10-20-fold greater than for ApUpG triplets. The interaction Rb + S was studied by following the changes in fluorescence anisotropy when labeled S1 reacted with ribosomes. The remaining two independent equilibrium constants (for S + T and RbT + S) were obtained from fits to observed anisotropy measurements when varying amounts of T were added to a solution of ribosomes and fluorescently labeled S1. This indirect procedure allows one to measure S + T binding, an association that is difficult to determine directly. Over the concentration interval 5-10 mM Mg2+, the association constant for Rb + S increases with the sixth power of [Mg2+], whereas the association constant for S + T decreases approximately 2-fold as Mg2+ is increased from 6 to 10 mM Mg2+. T binds to Rb more tightly at 10 mM than at 6 mM Mg2+. When S1 is bound to Rb, however, at 10 mM Mg2+ the binding constant for T is decreased 10-fold and the Mg2+ dependence is reversed. These interactions can be described in terms of coupling free energies. For the ternary complex, three linearly independent coupling free energies can be written.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1983

The binding of ribosomal protein S1 to S1-depleted 30S and 70S ribosomes. A fluorescence anisotropy study of the effects of Mg2+.

We have determined the equilibrium constants for the binding of AEDANS-labelled S1 to S1-depleted 30S and 70S ribosomes. For "tight" ribosomes, the association of S1 increases with the sixth power of Mg2+ concentration, but for 30S subunits and "loose" ribosomes, there is virtually no dependence of the association on Mg2+ over the same concentration range, 2-10 mM in Mg2+. The binding of S1 to 70S ribosomes at 10 mM Mg2+ is stabilized by 2 kcal/mol compared to the binding to 30S subunits. When intact S1 binds to tight ribosomes, the fluorescence anisotrophy is that for virtually complete rotational immobilization. The anisotropies vary considerably with the preparation and treatment of both S1 and ribosomes and these variations are detailed here. The results suggest the linkage of Mg2+-dependent conformational changes in the intact ribosomes, perhaps including rRNA, and the binding of S1.

Escherichia coli↗
PubMed1983

Purification and properties of the inhibitory protein isolated from Lactobacillus acidophilus AC1.

Lactobacillus acidophilus AC1 was found to produce a proteinic inhibitor having a molecular weight of 5.4 kd, active against both Gram-positive and Gram-negative bacteria. Some of the sensitive bacteria were found to be resistant to most of the commonly employed drugs and antibiotics. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of the purified inhibitor showed the presence of a single polypeptide. The inhibitor was active over a wide pH range from 4.0 to 7.5. It was heat sensitive, and complete inactivation occurred within 20 min at 50 degrees C. The purified inhibitor lost 50% of its activity within 24 h at room temperature and after 5 days at 4 degrees-8 degrees C. The inhibitory protein was readily distinguished from other inhibitors in lactic cultures by its immunological cross-reactivity.

Anti-Bacterial Agents↗
PubMed1982

Prodigiosin, a component of kappa phage receptor complex in Serratia marcescens.

Studies on kappa phage inactivation with isolated pigments from Serratia marcescens were carried out. Kappa phage is sensitive to inactivation with diethyl ether, petroleum ether, acetone and methanol, but is quite stable in chloroform and dimethyl sulphoxide. The pigment extract dissolved in chloroform inactivates about 50% of the total suspended phages. The pigment dissolved in acetone and dimethyl sulphoxide inactivates about 96.50% and 64.10% of the phages, respectively. High inactivation values with acetone were partially due to direct inactivation rather than the pigment itself.

Bacteriophages↗
PubMed1977

Phosphate uptake and involvement of binding protein in Tween-80 supplemented culture of Aspergillus fumigatus.

Tween-80 supplementation in submerged culture of Aspergillus fumigatus resulted in an increase of phosphate uptake. The uptake system was characterized as saturable, energy-dependent and operating against the concentration gradient. Control and Tween 80 cultures showed similar Km values for phosphate uptake (50 micrometer). Cold osmotic shock treatment of the cultures was found to cause considerable reduction in the ability to take up phosphorus with concomitant release of the binding protein into the shock fluid. Binding protein preparation from Tween-80 supplemented cells showed more activity than that from control cells.

Aspergillus fumigatus↗
PubMed1977

Moisture permeation of typical unit does repackaging materials.

The moisture permeation of unit does repackaging materials used by various hospital and community pharmacies in a metropolitan area was studied. Commercial desiccant pellets were packaged in the same manner used for ordinary tablets and capsules. The samples were weighed and placed in a controlled chamber at about 75% relative humidity and 22 C, and tested for weight gain over a period of 4-10 days. Four types of packages were evaluated: (1) heat-sealed polyethylene bag, (2) polyvinyl chloride cups adhesive-sealed to multiple-ply paper, (3) heat-sealed "polycel-polyfoil" strip packages and (4) polyvinyl chloride/foil multiple-cup blister packs. A wide range of results was found. None of the containers tested was a good moisture barrier, although some offered protection for a limited time. Several needs were identified by this survey. Pharmacists need more information and an increased awareness concerning the permeation characteristics of repackaging materials, suitable operating procedures and the stability of pharmaceutical products. Standards must be established for repackaging materials as well as limits on storage periods for the repackaged pharmaceuticals. Procedures for pharmacists to test their own packaging systems, and a checklist of some important guidelines for repackaging in unit dose containers, are presented.

Drug Packaging↗
PubMedDate not supplied

Magnetic resonance imaging of the superior oblique muscle in superior oblique myokymia.

High resolution, magnetic resonance imaging was used to quantitatively study the morphometry of the superior oblique muscles of two patients with superior oblique myokymia, as well as 18 superior oblique muscles of 14 patients with normal superior oblique function. The cross sectional area of each superior oblique muscle was measured at 3-millimeter intervals along the entire muscle length. In both cases of myokymia, the affected superior oblique muscles were significantly smaller than normal (P < .05). These anatomical changes in the superior oblique muscle of patients with myokymia suggest that an antecedent injury to the trochlear nerve has occurred. This injury, even if clinically unapparent, may be the initial event which leads to subsequent development of superior oblique myokymia.

Adult↗