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Biomedical subjects

L R Brown

Publications and source records attributed to L R Brown.

At least 127 records · Page 7Linked to original sources
PubMed1980

Physicochemical characterization of glucagon-containing lipid micelles.

Fluorescence studies showed that glucagon binds to a variety of micellar lipids. By means of ultracentrifugation and quasi-elastic light-scattering, it was found that stoichiometrically well defined complexes were formed between glucagon and perdeuterated dodecylphosphocholine micelles consisting of one glucagon molecule and approx. 40 detergent molecules. Well resolved 1H-NMR spectra were obtained for glucagon in the deuterated micelles. Studies of nuclear Overhauser effects between individually assigned protons in different regions of the amino acid sequence indicated that micelle-bound glucagon adopts a well defined, predominantly extended conformation. Evidence obtained from circular dichroism indicates that the conformation of glucagon bound to various micellar lipids is largely independent of the type of lipid and, furthermore, appears to be very similar to that of glucagon bound to lipid bilayers.

Chemical Phenomena↗
PubMed1980

High-resolution 1H-NMR studies of monomeric melittin in aqueous solution.

High resolution 1H-NMR at 360 MHz was used to characterize monomeric melittin in aqueous solution. The monomeric form of melittin was found to prevail at 3 mM concentration, pH 3.0, and temperatures between 30 and 90 degrees C, both in the absence of salt and with 6 M guanidium chloride. From comparison with model peptides and studies of the effects of 6 M guanidium chloride and variable temperature on the NMR parameters it was concluded that monomeric melittin is predominantly in an extended flexible form, with the fragments 5--9 and 14--20 more highly structured than the rest of the amino acid sequence. The appearance of a second, low abundant form of monomeric melittin, which is in slow exchange on the NMR time scale with both the more abundant monomeric conformation and aggregated melittin, was attributed to cis-trans isomerism of the peptide bond Leu-13--Pro-14.

Amino Acid Sequence↗
PubMed1980

High-resolution 1H-NMR studies of self-aggregation of melittin in aqueous solution.

4 mM melittin solution in 0.05 M sodium phosphate buffer at p2H 7.0 and 30 degrees C was shown by ultracentrifugation to contain tetrameric melittin. Using the spectra of this species and the previously characterized monomeric melittin as references, high-resolution 1H-NMR at 360 MHz was used to investigate self-aggregation of melittin at variable temperatures, pH and ionic strength. The NMR parameters show that the spatial structure of aggregated melittin is different from monomeric mellitin in aqueous solution but resembles closely the conformation adopted by melittin bound to detergent micelles. Comparison of melittin bound to different detergent micelles and self-aggregated melittin in different aqueous media indicates that the mellitin monomers adopt similar conformations in all these systems. The present data suggest that melittin assumes an amphiphilic spatial structure which is stabilized both by the formation of mixed micelles with detergents or by self-aggregation.

Amino Acid Sequence↗
PubMed1980

Transcription of exogenous and endogenous deoxyribonucleic acid templates in cold-shocked Bacillus subtilis.

Ribonucleic acid (RNA) synthesis was examined in cold-shocked Bacillus subtilis cells. The cells were grown to mid-log stage, harvested, and cold shocked. RNA synthesis was monitored by the incorporation of [3H]uridine triphosphate or [alpha 32P]adenosine triphosphate into trichloroacetic acid-precipitable material in the presence of all four nucleoside triphosphates. The inhibition of RNA synthesis in cold-shocked cells by lipiarmycin, ethidium bromide, rifampin. or streptolydigin was analyzed using mutant or wild-type cells. Also examined were the effects of temperature, salt concentration, and the addition of polyamines or highly phosphorylated nucleotides. In ultraviolet-irradiated and cold-shocked cells, RNA wynthesis decreased to low levels. The addition of exogenous phi 29 or TSP-1 template to these cells caused a 13- to 20-fold increase in RNA synthesis, as monitored by trichloroacetic acid-precipitable counts. RNA synthesized in the presence of phi 29 deoxyribonucleic acid (DNA) hybridizes mainly to EcoRI fragments A and C of phi 29 DBA, These two fragments direct transcription by purified RNA polymerase in vitro and hybridize to early phi 29 DNA produced in vivo. Our results with TSP-1 DNA in this system indicated that the RNA produced hybridizes to the same fragments as early RNA produced in vivo. Plasmic pUB110 DNA was not transcribed in this system.

Bacillus subtilis↗
PubMed1980

Fluoride resistance and adherence of selected strains of Streptococcus mutans to smooth surfaces after exposure to fluoride.

The fluoride resistance and smooth surface adherence characteristics of Streptococcus mutans were examined using tooth model and radioactive cell assays. Resistance to 600 ppmF by S. mutans isolated from the plaque of radiation-induced xerostomia patients receiving daily topical applications of a caries preventive 1% NaF gel was transient. Resistance induced in vitro in two strains of S. mutans by exposure to gradually increasing levels of NaF was apparently permanent. Smooth surface adherence by both fluoride-sensitive and -resistant strains of S. mutans 6715 in a tooth model system was slightly diminished by 1% NaF gel. Fluoride-resistant strains retained 89 to 93% of their adherence capability in 600 ppmF, as determined by the cell radiolabeling assay.

Adhesiveness↗
PubMed1980

Effect of sodium fluoride on the viability and growth of Streptococcus mutans.

A fluoride-sensitive (FS) strain of Streptococcus mutans and a laboratory-induced fluoride-resistant (FR) offspring were compared for the effects of sodium fluoride on viability and growth. There was a significant fluoride-related loss of viability in resting cell suspensions of the FS strain during a 47-hour exposure to fluoride levels above 75 ppm that was not encountered with the FR strain. The addition of 300 ppmF to actively growing six-hour broth cultures almost totally arrested the growth of the FS strain, while only slightly reducing that of the FR culture. The addition of 600 ppmF immediately terminated FS growth, and greatly reduced the rate and maximum growth of FR cultures.

Cell Division↗
PubMed1980

Comparison of the predominant cultivable microflora in the dental plaque of Macaca mulatta (rhesus) and Macaca fascicularis (cynomolgus).

The predominant cultivable bacteria in the supra-gingival plaque of Old World monkeys were similar to those in human plaque. A significant interanimal species difference was observed in the absolute and relative concentration of specific microbial populations. Streptococcus mutans serotype c was found primarily in rhesus plaque and serotype e in cynomolgus plaque.

Actinomyces↗
PubMed1980

Radiographic detection of thymoma.

Among 69 cases of thymoma, 16 of the lesions were not detected immediately in the first Mayo Clinic posteroanterior radiographs. Often they resembled right heart enlargement, their margins overlay the shadow of the right heart or hilus, or they were too small to be seen. A helpful sign was lobulation of the mass. Used selectively within the series, lateral views, computed tomography (CT), oblique views guided by fluoroscopy, and plain-film tomography contributed variously to accuracy of diagnosis and description. Until a determination is made, application in the order listed is recommended. Lateral tomograms often showed details of small, isolated abnormalities in the anterior mediastinum. Although CT did not reveal any lesions that were not suspected from other radiographic studies, it did show important anatomic relations. Early detection is important: 29% of the lesions were malignant, including 22% of those smaller than 5 cm. However, diagnosis was delayed after initial radiologic investigation (either elsewhere or at Mayo Clinic) in 17 cases (25% of the series), for intervals averaging 41 months. None of the imaging techniques was accurate in predicting malignancy, although CT best demonstrated adherence and invasion.

Aged↗
PubMed1979

Use of fully deuterated micelles for conformational studies of membrane proteins by high resolution 1H nuclear magnetic resonance.

Micellar complexes of melittin with fully deuterated detergents have been studied by high resolution 1H nuclear magnetic resonance (NMR). The synthesis of deuterated micelles is described and it is shown that the 1H NMR spectrum of micelle-bound melittin is well resolved and suitable for detailed analysis by conventional high-resolution NMR methods. A preliminary characterization of micelle-bound melittin shows that interaction with the micelle results in different conformational and dynamic features for the hydrophobic and hydrophilic regions of the melittin amino acid sequence. The present experiments on melittin and preliminary results with other polypeptides and proteins demonstrate that in favourable cases high-resolution 1H NMR studies of the complexes formed between membrane proteins and deuterated micelles provides a viable method for conformational studies of membrane-bound proteins.

Bee Venoms↗
PubMed1979

Physicochemical studies of the protein-lipid interactions in melittin-containing micelles.

Complexes of melittin with detergents and phospholipids have been characterized by fluorescence, circular dichroism, ultracentrifugation, quasi-elastic light scattering and 1H nuclear magnetic resonance (NMR) experiments. By ultracentrifugation and quasi-elastic light-scattering measurements it is shown that melittin forms stoichiometrically well-defined complexes with dodecylphosphocholine micelles consisting of one melittin molecule and approximately forty detergent molecules. Evidence from fluorescence, circular dichroism and 1H nuclear magnetic resonance experiments indicates that the conformation of melittin bound to micelles of various detergents or of diheptanoyl phosphatidylcholine is largely independent of the type of lipid and furthermore appears to be quite closely related to the conformation of melittin bound to phosphatidylcholine bilayers. 1H NMR is used to investigate the conformation of micelle-bound melittin in more detail and to compare certain aspects of the melittin conformation in the micelles with the spatial structures of monomeric and self-aggregated tetrameric melittin in aqueous solution. The experience gained with this system demonstrates that high resolution NMR of complexes of membrane proteins with micelles provides a viable method for conformational studies of membrane proteins.

Bee Venoms↗
PubMed1979

Corneal edema with several hard corneal contact lenses.

Five patients were each fitted with polymethylacrylate (PMMA), BP Flex, and Polycon corneal contact lenses of the same dimensions. Corneal edema was monitored with a slit-lamp biomicroscope and pachometer. Lenses were worn in a double-masked and random sequence for periods of 6 hr. Patients developed less corneal edema with Polycon lenses than with PMMA lenses. There was no significant difference in corneal edema with PMMA and BP Flex lenses. Those patients who developed little corneal edema with optimum-fitting PMMA lenses also developed little edema with the BP Flex and Polycon lenses. Steeper-fitting PMMA and BP Flex lenses produced more corneal edema than optimum-fitting lenses made of the same materials, while steeper-fitting Polycon lenses produced only slightly more edema than the optimum-fitting Polycon lenses.

Adult↗
PubMed1979

Comparison of the plaque microflora in immunodeficient and immunocompetent dental patients.

The nature and extent of the immune dysfunctions in 20 immunodeficient patients, as well as the immunocompetence of 22 control subjects, were verified by cell-mediated responsiveness and immunoglobulin quantitations. Comparisons of the microbial composition of supragingival plaque between the two populations showed that a greater number of immunodeficient than control subjects harbored Candida sp. and Staphylococcus sp. Conversely, a lower number of immunodeficient than control subjects harbored Streptococcus mutans. Also, patients with immune dysfunctions had a lower dental caries experience than their immunocompetent counterparts.

Antibody Formation↗
PubMed1978

Systemic artery-to-pulmonary vein fistula in osteogenic sarcoma of the chest wall.

An arteriovenous fistula between the systemic and pulmonary circulations may be congenital, as in bronchopulmonary sequestration, or the communication may be acquired. Inflammatory disease, trauma, and, rarely, neoplasm have been implicated as possible causes of acquired communications. We describe a patient who had a systemic artery-to-pulmonary vein fistula that was secondary to a recurrent sarcoma of the chest wall. Review of the literature failed to reveal a previous report of a similar case.

Adult↗
PubMed1978

Transconjugant analysis: limitations on the use of sequence-specific endonucleases for plasmid identification.

We used the sequence-specific endonucleases EcoRI, SmaI, BamHI, HsuI, and HaeIII as identification tools in following the conjugal transfer of the well-studied R plasmids Sa, R388, RP4, and R6K. Transfers were both intergeneric and intrageneric. Plasmid fingerprints were generated from both single- and combination-enzyme digests. The Sa transconjugants yielded plasmids showing consistent fingerprints for each of the respective endonucleases used, whereas the three other R-plasmid transconjugants showed fingerprint changes.

Base Sequence↗