Search PubMed⌕ Search

Biomedical subjects

K Leonard

Publications and source records attributed to K Leonard.

88 records · Page 5Linked to original sources
PubMed1982

Ribosomal crystalline arrays of large subunits from Escherichia coli.

Crystalline sheets of the 50S ribosomal subunits of Escherichia coli have been formed in vitro. Electron micrographs of these arrays diffract to 35-angstrom resolution. The lattice parameters of the crystals are a = 330 +/- 20 angstroms, b = 330 +/- 30 angstroms, and alpha = 123 degrees +/- 5 degrees, and the space group is most likely p21. These arrays of ribosomal subunits are sufficiently ordered to resolve such known features of the large ribosomal subunit as the L7/L12 stalk and the central protuberance.

Crystallography↗
PubMed1981

Membrane-bound and water-soluble cytochrome c1 from Neurospora mitochondria.

Cytochrome c1 is a subunit of ubiquinol--cytochrome c reductase (EC 1.10.2.2). In Neurospora crassa wild type 74A grown in the presence of chloramphenicol, the subunit is inserted only into the bilayer of the mitochondrial inner membranes without associating with other proteins. From these modified membranes a monodisperse (cytochrome c1)-Triton complex was isolated by subjecting the Triton-solubilized membranes to affinity chromatography on immobilized cytochrome c. A water-soluble pentamer of cytochrome c1 was prepared from the (cytochrome c1)-Triton complex by removing the detergent. By limited proteolytic digestion of the cytochrome c1-Triton complex with chymotrypsin, a water-soluble monomeric cytochrome c1 was prepared which has a molecular weight of only 24 000 as compared to 31 000 of the membrane-bound cytochrome c1. The 24 000-Mr cytochrome c1 and the 31 000-Mr cytochrome c1 have same light absorption spectra and cytochrome-c-binding properties. These results are used to propose the following model. Cytochrome c1 consists of a large hydrophilic part and a small hydrophobic part. The hydrophilic part extends from the mitochondrial inner membrane into the intermembrane space. This part carries the heme and interacts with cytochrome c. The hydrophobic part anchors the cytochrome c1 to the bilayer.

Amino Acids↗
PubMed1978

Formation of protein micelles from amphiphilic membrane proteins.

The membrane penicillinase (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6) from Bacillus licheniformis, the Semliki Forest virus spike proteins, and the Sendai virus glycoproteins have each been isolated as soluble protein aggregates that are virtually free of lipid and detergent. The sedimentation coefficients of the complexes were 18 S, 29 S, and 43 S, respectively. Mixed aggregates containing both the virus glycoproteins and the penicillinase could also be formed. Such protein micelles may serve a number of useful purposes in membrane research.

Antibodies↗
PubMedDate not supplied

The Staphylococcus aureus alpha-toxin channel complex and the effect of Ca2+ ions on its interaction with lipid layers.

Using the techniques of two-dimensional crystallization on supported lipid bilayers together with computer image processing, two distinct two-dimensional crystal types of staphylococcal alpha-toxin complex are formed depending on the presence or absence of Ca2+ ions. Without Ca2+, these are hexagonally packed (in A, a = b = 89.5 +/- 2.5 A; theta = 119.7 degrees) With Ca2+ present, rectangular crystal packing is seen (in A, a = 114.8 +/- 1.6 A, b = 140.2 +/- 0.7 A; theta = 89.1 degrees). A third, banded crystal type is also seen which is interpreted as a side-to-side packing of regular tubules. We use these tubular crystals for cross-correlation searches with top and side-on views of the complex from single particle reconstructions, and with the repeating units from the two-dimensional crystal types. The results lead us to propose a model in which the different two-dimensional crystal types are formed as a result of alpha-toxin hexamers packing in different orientations. In the hexagonal crystals the hexamers lie end-on with a 6-fold axis in projection. On the addition of Ca2+, the hexamers reorient to lie tilted with respect to the support, thus giving rise to a rectangular projection.

Bacterial Toxins↗
PubMedDate not supplied

Alloimmunization after granulocyte transfusions.

BACKGROUND: Although granulocyte transfusions are recommended for neutropenic patients with bacterial infections that are unresponsive to antibiotic therapy, the presence of white cell (WBC) antibodies in the recipient can render these transfusions ineffective. STUDY DESIGN AND METHODS: A 25-year-old man with chronic granulomatous disease experienced a pulmonary transfusion reaction while receiving granulocyte transfusions, and he was found to be immunized to neutrophil antigen NA2. A retrospective study of alloimmunization to HLA and neutrophil antigens in 18 patients with chronic granulomatous disease who had also received repeated granulocyte transfusions was then performed. Sera were tested in lymphocytotoxicity, granulocyte agglutination, granulocyte immunofluorescence, monoclonal antibody immonobilization of granulocyte antigen, and immunoprecipitation assays. RESULTS: After the granulocyte transfusions, sera from 14 of the 18 patients contained WBC antibodies. Seven sera samples reacted in the lymphocytotoxicity, granulocyte immunofluorescence, and granulocyte agglutination assays; seven reacted in the lymphocytotoxicity and granulocyte immunofluorescence assays but not the granulocyte agglutination assay, and four did not react. When the monoclonal antibody immobilization of granulocyte antigen assay was used, three sera samples reacted with Fc gamma receptor III, three with the 58- to 64-kDa protein carrying the neutrophil antigen NB1, one with CD11a, and one with CD18. Antibodies from three patients immunoprecipitated a neutrophil protein of 60 kDa. Overall, antibodies to neutrophil antigens other than HLA could be detected in sera from eight patients. Transfusion reactions occurred in 11 of the 14 individuals with WBC antibodies and in none of the 4 without antibodies. Seven pulmonary reactions occurred in patients with WBC antibodies. The patients with WBC antibodies were given significantly more granulocyte concentrates (78 +/- 65 vs. 29 +/- 15 units, p < 0.05). CONCLUSION: Recipients of granulocyte transfusions often become alloimmunized. Screening for WBC antibodies periodically during transfusions, after adverse reactions, or before subsequent transfusions is indicated. If WBC antibodies are present, no further granulocyte transfusions should be given unless the granulocytes are collected from HLA- and/or neutrophil antigen-compatible donors.

Adolescent↗
PubMedDate not supplied

Case-control study of sexually transmitted diseases as cofactors for HIV-1 transmission.

The aim of the study was to investigate the association between infection with HIV-1 infection and a history of other sexually transmitted diseases (STD). We were able to match 1295 HIV-1 infected patients who attended St Mary's Hospital between 1985 and 1991 with 1273 seronegative controls on gender, sexual orientation, injecting drug use and age at time of test. The cases were 3 times more likely to have a history of ever having had another STD than the controls: multivariate conditional logistic regression showed that, after controlling for sexual behaviour, for known sexual contact with an HIV infected individual or AIDS patient or with a resident from a high HIV prevalence area, area of residence and for year of test, a history of gonorrhoea, syphilis, hepatitis B, genital herpes or genital warts were all significantly associated with HIV-1 seropositive status. These findings reinforce the need for HIV containment strategies to be promoted in conjunction with containment programmes for others STDs.

Adult↗