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Biomedical subjects

L Brooks

Publications and source records attributed to L Brooks.

At least 73 records · Page 4Linked to original sources
PubMed1990

Role of arginine 67 in the stabilization of chymotrypsin inhibitor 2: examination of amide proton exchange rates and denaturation thermodynamics of an engineered protein.

We have examined the contribution to protein stability of an interaction involving a charged hydrogen bond from an arginyl side chain (Arg67) in the serine proteinase inhibitor chymotrypsin inhibitor 2 (CI-2), by replacing this side chain with an alanyl residue by protein engineering. Using nuclear magnetic resonance spectroscopy (NMR), we have examined the effect of this mutation on the hydrogen-deuterium exchange rates of several backbone amide protons in the native and engineered proteins at 50 degrees C. These exchange rates provide a localized probe at multiple discrete sites throughout the protein and from comparison of native and mutant exchange rates allow calculation of the difference in free energy of exchange (delta delta Gex) resulting from the mutation. The results show that for the majority of amides observed this mutation results in delta delta Gex of ca. 1.7 kcal mol-1 over the whole CI-2 molecule. However, for two relatively exposed amide protons the exchange rates are found to be far less perturbed, implying that local unfolding mechanisms predominate for these protons. Direct measurement of the stability of both proteins to denaturation by guanidinum hydrochloride shows that the interaction contributes 1.4 kcal mol-1 to the stability of the molecule. This value is comparable to those obtained from the NMR exchange measurements and indicates that the exchange processes reflect the differences in stability between the native and mutant proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine↗
PubMed1990

Sulfonamide resistance gene for plant transformation.

The sulfonamide resistance gene from plasmid R46 encodes for a mutated dihydropteroate synthase insensitive to inhibition by sulfonamides. Its coding sequence was fused to the pea ribulose bisphosphate carboxylase/oxygenase transit peptide sequence. Incubation of isolated chloroplasts with the fusion protein synthesised in vitro, showed that the bacterial enzyme was transported to the chloroplast stroma and processed into a mature form. Expression of the gene fusion in transgenic plants resulted in a high level of resistance to sulfonamides. Direct selection of transformed shoots on leaf explants was efficient using sulfonamides as sole selective agents. Transformed shoots rooted normally on sulfonamides at concentrations toxic for untransformed ones. Sulfonamide resistance was transmitted to the progeny of transformed plants as a single Mendelian dominant character. These results demonstrate that this chimeric gene can be used as an efficient and versatile selectable marker for plant transformation.

Amino Acid Sequence↗
PubMed1990

Expression of the sulfonamide resistance gene from plasmid R46.

The expression of the sul I gene from plasmid R46, a wide host range plasmid of the IncN incompatibility group, was studied in Escherichia coli. Using a promoter test vector, a promoter was detected upstream of the sul I gene. From a nuclease protection experiment, the transcription was determined to start 360 bp upstream of the coding sequence. Two putative promoter -35 and -10 sequences were found upstream from the predicted transcription start. The presence of this promoter sequence in other R factors was discussed in relation with previous data showing that the sul I genes were transcribed from other promoters. The translation product of the sul I gene was detected in minicells. Its size indicates that the translation starts at the first ATG codon found in the open reading frame.

Base Sequence↗
PubMed1989

Epstein-Barr virus gene expression in malignant lymphomas induced by experimental virus infection of cottontop tamarins.

Inoculation of cottontop tamarins with a large dose of Epstein-Barr virus (EBV) leads to the induction of multiple EBV genome-positive lymphomas. These tumors have been characterized as oligoclonal or monoclonal large-cell malignant lymphomas that closely resemble the EBV genome-positive B-cell lymphomas that arise in human allograft recipients. The expression of latent and lytic EBV-encoded proteins was investigated in these virus-induced tamarin lymphomas and in derived cell lines. The tamarin tumors were found to express EBV nuclear antigen 1 (EBNA 1), EBNA 2, EBNA leader protein, and the latent membrane protein (LMP) as determined both by immunohistochemical staining and by immunoblotting. However, within the limits of the immunoblotting assays, no expression of the EBNA 3a protein family could be detected. Assays for lytic-cycle proteins by using both polyclonal human sera and monoclonal antibodies against viral capsid antigen, early antigen, and membrane antigen (gp340/220) showed minimal, if any, expression of these antigens in the lymphoma biopsies. In contrast, the cell lines derived from these lymphomas, even in early passage, expressed abundant levels of the lytic-cycle antigens and also expressed the EBNA 3a protein as well as EBNA 1, EBNA 2, EBNA leader protein, and LMP. This finding suggests that the virus-lymphoma cell interaction, in particular the switch to lytic cycle, is subject to some form of host control in vivo. The expression of EBNA 2 and LMP in these tamarin lymphomas strengthens their resemblance to posttransplant lymphomas in humans, since these human tumors are also EBNA 2 and LMP positive (L. S. Young, C. Alfieri, K. Hennessy, H. Evans, C. O'Hara, K. Anderson, A. Rickinson, E. Kieff, and J. I. Cohen, submitted for publication). Since both proteins are known to be important effector molecules of virus-induced B-cell growth transformation in vitro, their expression in these lymphomas constitutes the best evidence for a direct oncogenic role for EBV in vivo.

Animals↗
PubMed1987

Retinal vasculitis in Crohn's disease.

Although systemic vasculitis is a prominent part of the extraintestinal complications of Crohn's disease, the association of a retinal vasculitis with this chronic granulomatous disease of the gastrointestinal system is rare. We examined a 26-year-old woman with biopsy-proven Crohn's disease who developed a severe bilateral, obliterative retinal arteritis and phlebitis, leading to a marked loss of vision. Treatment with systemic corticosteroids and cyclophosphamide succeeded in halting progression of the disease.

Adult↗
PubMed1985

Iron exclusion from aflatoxin B1-induced hepatocellular carcinoma in rats.

Mixed-cell hepatocellular adenocarcinomas, induced by aflatoxin B1 (AFB1) in weanling rats, were allowed to develop for 18 months; age- and sex-matched controls were maintained. After 18 months, treated and control rats were administered iron dextran (ID), intraperitoneally (i.p.) as Nonemic. No gross or microscopic lesions were observed in control animals, while hepatic tumors were observed grossly in all AFB1-treated rats. Areas of apparently normal tissue, in histologic sections from control animals and in non-tumor sites of sections from AFB1-treated animals, were deeply stained for iron, both in endothelial cells and in hepatocytes, as visualized by Perls iron stain. Varying degrees of exclusion of stainable iron material were noted in histologic sections of lesions from AFB1-treated rats, as were alterations in endothelial cell staining characteristics. Iron staining clearly demonstrates the presence of varying cell populations within the induced mixed cell hepatocellular adenocarcinoma.

Adenocarcinoma↗
PubMed1982

Torsio appendicis vermiformis. Report of an unusual case.

Torsion of the appendix vermiformis is a rare condition, that clinically simulates an acute appendicitis with sudden severe symptoms. This report describes a case of a 540-degree twisted appendix, that gave rise to prolonged, vague symptoms. This clinical picture has not been described before.

Appendix↗
PubMed1981

The effect of inhalation of nebulized steroid on the acid aspiration syndrome.

The effects of acid aspiration on lung mechanics, gas exchange, haemodynamics and lung water, and their modification by nebulized dexamethasone were studied in 10 dogs. Each dog received 0.1 N HCl pH of 1.0 (15 ml/l vital capacity), instilled down the tracheal tube. PEEP 0.98 kPa (10 cm H2O) was introduced 20 minutes after aspiration and was continued until the completion of experiment. Treated animals (N = 5) received dexamethasone 5 mg . kg-1 by continuous nebulization over a two hour period starting 20 minutes after aspiration. Untreated (N = 5) animals received nebulized saline. Measurements were taken before aspiration and at 20 minutes 2.5 and 5.0 hours after aspiration. Red blood cells labelled with 51Cr were injected before sacrifice. After sacrifice multiple lung samples were taken for measurement of pulmonary extravascular water (PEW) by the gravimetric technique. Acid aspiration caused significant changes in lung volumes, PaO2, and intrapulmonary shunt. Pulmonary extravascular water was 6.16 +/- 0.93 ml/g dry tissue in treated and 6.47 +/- 0.60 ml/g dry tissue in untreated animals. These results indicate the presence of severe pulmonary oedema. There were no significant differences in any measured parameter between treated and untreated animals. We conclude that nebulized dexamethasone is of no value in treatment of the acute changes induced by acid aspiration.

Animals↗