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U Sinha

Publications and source records attributed to U Sinha.

17 recordsLinked to original sources
PubMed1992

Expression, purification, and characterization of inactive human coagulation factor Xa (Asn322Ala419).

We have expressed in Chinese hamster ovary cells a catalytically inactive form of human factor Xa (factor rXai). A recombinant precursor of human factor Xa was inactivated by two point mutations in the serine protease catalytic triad, Asp322Asn and Ser419Ala. A two-step purification to homogeneity of the secreted material involved immunoaffinity followed by heparin-agarose chromatography. Two forms were identified; a fully processed dimer (70%) and a partially processed monomer (30%). Limited N-terminal amino acid sequencing of factor rXai detected the predicted residues and gamma-carboxyglutamic acid content was 90% of human plasma control. Although devoid of measurable proteolytic activity, factor rXai competitively inhibited plasma factor Xa assembly into functional prothrombinase complexes (Ki = 3 x 10(-10) M). Factor rXai also inhibited plasma clotting in a dose-dependent manner. The possible use of recombinant catalytically inactive proteins as a general approach for pharmacological regulation of human diseases is discussed.

Amino Acid Sequence↗
PubMed1992

Magnetic resonance image synthesis from analytic solutions of spin-echo and radio frequency-spoiled gradient-echo images.

RATIONALE AND OBJECTIVES: To synthesize magnetic resonance images (MRI) in real-time using a minimal data set obtained with routine clinical protocols and stored in a picture archiving and communication system (PACS) database. METHODS: Analytic solutions for T1 and T2 were obtained from a double and a single spin-echo set, with routine parameters. Analytic solutions from radio frequency-spoiled gradient-echo images, with TRs as low as 33 mseconds, also were used to synthesize gradient-echo images. RESULTS: Phantom studies showed that the errors in the synthesized images were significantly smaller than the errors in the T1- and T2-calculated images and similar to the source images. The gradient-echo images resulted in significant scan time savings. CONCLUSION: MRI synthesis from analytic solutions of T1, T2, and rho saves computational time and yields accurate values for the intrinsic parameters while allowing the use of routine clinical protocols. The availability of clinical images in the PACS database and the ability to synthesize images in real-time has allowed the development of a practical interactive teaching module.

Brain↗
PubMed1992

Radionecrosis secondary to interstitial brachytherapy: correlation of magnetic resonance imaging and histopathology.

Radiation-induced tissue damage in the central nervous system is a well-known complication of interstitial brachytherapy for brain tumors, yet imaging correlates have historically been based upon computed tomographic scans. We now present magnetic resonance imaging (MRI) to correlate radiation changes after interstitial brachytherapy with the histopathology. The central nervous system of a 38-year-old man with a left frontal cerebral glioma diagnosed by stereotactic biopsy was treated with interstitial brachytherapy (iridium-192, 47 Gy), followed by limited-field irradiation (45 Gy). With progressive deterioration, a second biopsy demonstrated radiation changes. Despite aggressive medical management, the patient died 9 months after completion of radiation therapy. Postmortem evaluation compared MRI scans of the intact, fixed brain with the histopathology. Axial sections (10 mm) obtained by MRI scan and autopsy brain slices were cut in the identical plane. Neuroimaging and histopathological findings of the lesion correlated within 2 to 3 mm resolution. In the peripheral white matter, MRI scan did not indicate the extent of radiation effect histologically. We suggest that MRI has limited utility in assessing the extent of impact of radiation on surrounding brain.

Adult↗
PubMed1992

A PACS-based interactive teaching module for radiologic sciences.

This article describes an interactive teaching module, linked to a picture archiving and communications system (PACS) data base, for teaching radiology. The module is currently tailored to MR images but can be adapted to any other imaging technique. An algorithm has been developed that allows the use of MR images acquired with routine clinical protocols and stored in the data base to yield, in real time, images at any other arbitrary TE and TR. In the browse mode, the user can study either the effect of different scan parameters or clinical cases on synthesized or acquired images. The quiz mode has multiple-choice questions and answers, accompanied by images. In the teaching mode, the instructor has access to the clinical data base and WRITE privileges for setting up the browse or quiz mode. The module achieves considerable flexibility when linked to the PACS, with access to all archived images and the ability to subsequently synthesize MR images at arbitrary TE and TR values in real time. The module is also "dynamic" in character, in that the instructor can easily add new cases and comments to the teaching files, both to enhance its clinical aspects and to reflect advances in technology.

Algorithms↗
PubMed1991

Design of constructs for the expression of biologically active recombinant human factors X and Xa. Kinetic analysis of the expressed proteins.

Activation of vitamin K-dependent plasma proteases occurs by specific interaction with components of the blood coagulation cascade. In this report, we describe the direct expression and enzymatic characterization of the human coagulation zymogen factor X and its activated form, factor Xa, from transformed Chinese hamster ovary fibroblast cell lines. Expression was achieved using either a full-length factor X cDNA or a unique mutant factor Xa cDNA. The functional factor Xa precursor contained a novel tripeptide bridge in place of the native 52-amino acid activation peptide. This mutation allowed for intracellular processing and secretion of the activated form of factor X. Secreted recombinant factors X (rX) and Xa (rXa) were purified by sequential anion-exchange and immunoaffinity chromatography. The enzymatic activities of factors rX and rXa were compared with those of plasma factors X and Xa in three independent assay systems. In comparison to human plasma factor X, the amidolytic, prothrombinase complex, and plasma clotting activities of factor rX were 50, 85, and 43%, respectively. The corresponding comparative activities for factor rXa were 32, 64, and 48%, respectively. The ability to directly express mutant forms of biologically active human factor X will facilitate the structure/function analysis of this important blood coagulation protein and may lead to the development of novel coagulation inhibitors.

Animals↗
PubMed1991

Two new extracellular serine proteases from Streptomyces fradiae.

1. Two new extracellular serine proteases have been purified to homogeneity from Streptomyces fradiae. 2. On amino acid sequencing, striking homology is observed between the first enzyme and Streptomyces griseus Protease A, and the second enzyme and S. griseus trypsin. 3. The sequence information shows for the first time that structurally and enzymatically related serine proteases are extracellularly expressed by different Streptomycetes. 4. Differential keratinolytic substrate specificity among these two microbes are probable due to a difference in disulfide reduction capacity.

Amino Acid Sequence↗
PubMed1988

Characterization of sheep alpha-1-proteinase inhibitor. Important differences from the human protein.

The plasma proteinase inhibitor corresponding to alpha-1-proteinase inhibitor (alpha 1Pl) in humans was isolated from sheep plasma. Ovine alpha 1Pl is of higher molecular weight (62,000 daltons) than is human alpha 1Pl, is resistant to chemical oxidation by N-chlorosuccinimide, and has poor elastase-inactivating power compared with the corresponding inhibitor in humans. However, ovine alpha 1Pl is a potent trypsin inhibitor. Despite the differences indicated above, a partial homology (22 to 35%) exists between human and sheep alpha 1Pl, at least as analyzed through the first 20 residues of the sheep inhibitor. The weak elastase-inhibitory capacity of sheep alpha 1Pl is paralleled by the low content of elastase in the sheep neutrophil granule. These important differences between sheep and human neutrophils and plasma proteinase inhibitors should be borne in mind in designing experiments related to proteolytically mediated lung injury in the former species.

Amino Acid Sequence↗
PubMed1987

Demonstration of an altered phenylalanyl-tRNA synthetase in an analogue-resistant mutant of Aspergillus nidulans.

We have isolated and characterized a new class of p-fluorophenylalanine (FPA)-resistant mutant in Aspergillus nidulans using a phenA strain as the wild type, by optimizing the conditions of growth. All four spontaneous mutants selected on a medium containing FPA were found to be recessive to their wild-type alleles in heterozygous diploids. Complementation analyses and linkage data showed that they were allelic and mapped at a single locus (fpaU) in the facA-riboD interval on the right arm of linkage group V. Partial purification and characterization of Phe-tRNA synthetase from wild-type and mutant strains revealed that the mutant enzyme had a greatly reduced ability to activate the analogue. It is suggested that mutation in the fpaU gene brings about a structural alteration in Phe-tRNA synthetase.

Amino Acyl-tRNA Synthetases↗
PubMed1986

Yeast enolase carboxyl modification using Woodward's reagent K.

Yeast enolase is inactivated by Woodward's reagent K. Substantial protection is afforded by binding of 1 mol of "conformational" metal ion/subunit. Inactivation is correlated with modification of 13 carboxyl groups/subunit in the absence of conformational metal ion and 17 in its presence. Ten tryptic peptides labeled by Woodward's reagent K can be isolated, mostly from the C-terminal half of the protein. The changes in reactivity of these peptides produced by conformational metal ion suggest direct coordination to Glu-181 together with a contraction of the protein.

Amino Acids↗
PubMed1985

A spectrophotometric method for quantitation of carboxyl group modification of proteins using Woodward's Reagent K.

Reaction of proteins with Woodward's Reagent K in 0.05 ionic strength Tris-HCl, pH 7.8, followed by removal of excess reagent by chromatography on Sephadex G-25 in the same buffer, results in covalently attached chromophores with an absorption maximum at 340 nm and an extinction coefficient of 7000 M-1 cm-1. This absorbance can be used to quantitate the reaction of Woodward's Reagent K with carboxyl groups in proteins, provided sulfhydryl groups do not react. The chromophore also enables specific detection and identification of carboxyl-modified peptides upon separation by chromatography or electrophoresis.

Indicators and Reagents↗
PubMed1976

Chloral hydrate induced haploidization in Aspergillus nidulans.

This is the first report of induction of haploidization in Aspergillus nidulans by chloral hydrate, which is an efficient polyploidizing agent for higher plants and a psychotropic drug for man. A new procedure has been described to isolate haploids from diploids with a very high frequency, as compared to p-fluorophenylalanine, which is generally used for this purpose.

Aspergillus nidulans↗
PubMedDate not supplied

Pulse sequence optimization for use with a biopsy needle in MRI.

The purpose of this study was to assess the degree of conspicuity and amount of field distortion caused by a biopsy needle designed specifically for use in MRI studies. Toward this, a number of pulse sequences including spin and field echo were used. Parameters such as field of view, strength of read gradient, direction of read gradient, echo time and slice thickness were varied. The effect of these manipulations on needle visualization was studied. Partial voluming errors with thicker slices decreased needle conspicuity. Smaller field of view improved needle visualization as a result of magnification effect. Shallow read gradient strengths also increased needle conspicuity. Increased image artifacts were noted on field-echo sequences compared to spin echo. This effect increased with longer echo times. This reflects T2* effects on field-echo images.

Biopsy, Needle↗
PubMedDate not supplied

Effect of field strength on susceptibility artifacts in magnetic resonance imaging.

In magnetic resonance imaging susceptibility artifacts occur at the interface of substances with large magnetic susceptibility differences, resulting in geometric distortions of the image at those boundaries. The susceptibility artifacts are often subtle on clinical images and if not carefully examined they may lead to misdiagnosis. Magnetic susceptibility artifacts are prevalent on the boundary of air-containing paranasal sinuses, as well as bone-soft tissue interfaces in the spinal canal. The appearance of these artifacts on images from three different magnetic field strength instruments, 0.3, 0.5, and 1.5 Tesla were studied. T1- and T2-weighted spin echo and gradient recalled echo pulse sequences were selected to image a water phantom containing substances of varying susceptibilities. The effects were also studied in MR images of the head in a normal human volunteer. At any given field strength the artifacts were more prominent in the gradient echo imaging than in the corresponding spin echo pulse sequence. As expected, the distortions were also greater at higher field strengths. The results in human subjects paralleled the findings in the phantom study.

Head↗
PubMedDate not supplied

PACS database architecture and design.

PACS (Picture Archiving and Communication Systems) database design requires careful understanding of the data and processing needs of radiologists, referring physicians, radiology staff, administrators, and researchers. Due to access requirements, the physical implementation for the management of small text data sets differs from the implementation strategy for large image data sets (centralized vs. distributed storage strategies). In this paper we discuss the database structure, storage architecture, file placement strategies, and administration considerations of the UCLA PACS.

Database Management Systems↗