PubMed Health⌕ Search

Biomedical subjects

M Sara

Publications and source records attributed to M Sara.

6 recordsLinked to original sources
PubMed2000

Aging, perception, and visual short-term memory for luminance-defined form.

The sensory, perceptual, and visual short-term memory (VSTM) capacity of young and older observers for processing luminance-defined shape information was assessed in a series of experiments. The following were assessed: each individual's threshold necessary to detect a square from its background as measured by luminance thresholds; the capacity for making simultaneous size discriminations when compensating for individual differences in sensory input; the capacity for making sequential size discriminations; and the capacity for remembering size differences over time. The results show a selective deficit for simultaneous perceptual processing for older subjects, which cannot be attributed to differences in sensory input, task difficulty, interhemispheric transfer, or VSTM.

Adult↗
PubMed1997

Expression of foreign proteins on the surface of Autographa californica nuclear polyhedrosis virus.

Based on the method of direct cloning into the baculovirus genome by linearizing and re-ligation in presence of the target insert, we designed viral constructs that express foreign genes on the surface of baculovirus particles. We chose the glycosylated envelope protein gp41 of human immunodeficiency virus type 1 (HIV-1) as a model for displaying recombinant proteins on budded virus. The ectodomain of the envelope protein gp41 of HIV-1 was being fused to the entire baculovirus major coat protein gp64 (Ac-cops41) and to the membrane anchor sequence of gp64 (Acmars41). Two different promoters, the "very late" polyhedrin promoter (Ac-mars41) and the "early and late" gp64 promoter (Ac-promars41) were compared. The expression of gp41 in infected cells and its presence on viral particles was confirmed by enzyme-linked immunosorbent assay (ELISA), Western blot and electron microscopy.

Animals↗
PubMed1996

Crystallization and preliminary X-ray analysis of a low density lipoprotein from human plasma.

Single crystals of human plasma low density lipoprotein (LDL), the major transport vehicle for cholesterol in blood, have been produced with a view to analysis of the three-dimensional structure by x-ray crystallography. Crystals with dimensions of approximately 200 x 100 x 50 microm have been reproducibly obtained from highly homogeneous LDL particle subspecies, isolated in the density ranges d = 1.0271-1. 0297 g/ml and d = 1.0297-1.0327 g/ml. Electron microscopic imaging of ultrathin-sectioned preparations of the crystals confirmed the existence of a regular, quasihexagonal arrangement of spherical particles of approximately 18 nm in diameter, thereby resembling the dimensions characteristic of LDL after dehydration and fixation. X-ray diffraction with synchrotron radiation under cryogenic conditions revealed the presence of well resolved diffraction spots, to a resolution of about 29 A. The diffraction patterns are indexed in terms of a triclinic lattice with unit cell dimensions of a = 16. 1 nm, b = 39.0 nm, c = 43.9 nm; alpha = 96.2 degrees, beta = 92.1 degrees, gamma = 102 degrees, and with space group P1.

Crystallography, X-Ray↗
PubMed1995

Laboratory-scale production and purification of recombinant HIV-1 reverse transcriptase.

HIV-1 reverse transcriptase from the HIV-1 strain WMF 1.13 was expressed in Escherichia coli JM 105 using a pKK233-2 vector. The bacteria were cultivated in a 20-l fermentor with 14-l net volume using M9ZB medium containing bactotryptone and yeast extract. After induction of reverse transcriptase (RT) expression by addition of isopropyl-beta-D-thiogalactopyranoside the enzyme concentration was monitored. Both soluble and inclusion-body deposited RT were detected by Western blots. Inclusion-body formation was confirmed by transmission electron microscopy. Further purification of soluble and insoluble RT was investigated. After cell desintegration by enzymatic treatment combined with osmotic shock and centrifugation, the supernatant was desalted by size-exclusion chromatography and further purified by DEAE-Sepharose FF, AF-Heparin Toyopearl 650 M and Fractogel EMD TMAE 650 (S). The results of the purification steps were monitored by SDS-PAGE with silver staining, non-radioactive RT assay and protein determination with Coomassie Blue. The sediment was extracted with 6 M GuHCl and after clarification and conventional refolding, treated in the same manner as soluble RT. This method is well suited for studying fermentation conditions as well as purification conditions. The RT is expressed in approximately equal amounts as soluble and insoluble enzyme.

Chromatography↗
PubMed1992

Scanning force microscopy studies of the S-layers from Bacillus coagulans E38-66, Bacillus sphaericus CCM2177 and of an antibody binding process.

In many prokaryotic cells (eubacteria and archaebacteria) the outermost cell envelope component is composed of a regularly structured protein surface layer (S-layer). The two-dimensional S-layer from Bacillus coagulans E38-66 and Bacillus sphaericus CCM2177 has been investigated by SFM at molecular resolution under physiological conditions (i.e., in buffer solution). We find the E38-66 S-layer lattice to be oblique with lattice parameters of a = 9-10 nm, b = 7-8 nm and gamma = 80 degrees -90 degrees (E38-66). The CCM2177 lattice is square with a = 12-14 nm, in good agreement with TEM data. We have used the unique possibility of the SFM to study the kinematics of biological processes and have performed experiments on the adhesion of polyclonal antibodies to the recrystallized E38-66 protein layer on a time scale of about two to ten seconds per image frame. This represents a first step in directly visualizing molecular recognition reactions.

Antibodies, Bacterial↗