Biomedical subjects

W Chiu

Publications and source records attributed to W Chiu.

132 records · Page 8Linked to original sources

PubMedDate not supplied

A 7-A projection map of frozen, hydrated acrosomal bundle from Limulus sperm.

The acrosomal bundle from Limulus sperm has been imaged to 7 A in a 400-kV electron cryomicroscope using the spot-scan technique. These images have been processed by Fourier averaging, corrected for the contrast transfer function, and merged to that resolution. The reconstructed density map of this projection shows features consistent with the 13-A projection map from a helical reconstruction and with the X-ray-derived model for F-actin, and regions of possible scruin-scruin contacts.

Acrosome↗

PubMedDate not supplied

PTOOL: a software package for the selection of particles from electron cryomicroscopy spot-scan images.

PTOOL, a suite of tools packaged in an X Window System-based graphical user interface has been developed to allow consistent and accurate selection of single particles from low-contrast spot-scan and flood beam electron microscopy images. These user friendly and computationally efficient tools run on Unix-based workstations. Particles are selected using an automatic reference based selection method which incorporates extensive image preprocessing. An image division and subsequent image sewing mechanism allows for efficient particle selection independent of micrograph size. A particle viewing tool is provided which displays galleries of images and has options for performing image processing operations such as Fourier filtering, histogram equalization, and image masking. In addition, a tool is included to perform semiautomatic focal pair particle matching to identify the same particles on two micrographs.

Bacteriophage P22↗

PubMedDate not supplied

CTF determination of images of ice-embedded single particles using a graphics interface.

We implement a graphical user interface in an X-window/UNIX environment to compute and display the incoherently averaged Fourier transforms of electron images of single particles embedded in ice and the simulated contrast transfer function with or without envelope functions. This interface provides an easy and efficient operation for the determination of defocus value and the evaluation of the extent of Fourier amplitude falloff. This computational procedure is crucial for prescreening image data and performing image correction of contrast transfer function in high-resolution three-dimensional reconstruction of single particles.

Capsid↗

PubMedDate not supplied

Effects of radiation damage with 400-kV electrons on frozen, hydrated actin bundles.

Electron images can be used to provide amplitudes and phases for the structural determination of biological specimens. Radiation damage limits the amount of structural information retrievable by computer processing. A 400-kV electron microscope was used to investigate radiation damage effects on frozen, hydrated actin bundles kept at -168 degrees C. The quality of phases within and among images in a damage series was evaluated quantitatively out to 16 A resolution. It was found that the phases of structure factors with good signal-to-noise ratio (IQ less than or equal to 4) can be reliably retrieved from images taken at a cumulative dose of at least 25 electrons/A2.

Actins↗

PubMedDate not supplied

Patch averaging of electron images of GP3*I crystals with variable thickness.

The combination of Fourier and correlation averaging techniques with multivariate statistical analysis and classification, a method known as patch averaging, is used to analyze untilted and tilted images of negatively stained GP32*I crystals, which exhibit variable thicknesses in a single crystal. Within a single image, coherent areas of the same apparent thickness can be distinguished from areas of differing thicknesses. Analysis using the phase relationships among symmetry-related reflections from reconstituted images obtained from untilted micrographs confirms the ability of the method to classify these variable thicknesses properly. Furthermore, the phases from some of the reconstituted images obtained from both untilted and tilted micrographs were found to match well with the phases in a previously determined three-dimensional data set of this crystal with pg symmetry along the crystallographic b axis. These results indicate the utility of the patch averaging procedures in the structural determination of protein crystals with different thicknesses.

Crystallization↗

PubMedDate not supplied

Hypertransfusion for spinal cord compression secondary to extramedullary hematopoiesis.

A 19-year-old girl with thalassemia intermedia presented with signs of thoracic spinal cord compression secondary to extramedullary hematopoiesis. She was started on a transfusion regimen to maintain a hemoglobin level of more than 12.5 g/dL. Clinical signs disappeared within the first week and circulating erythroblastemia was completely suppressed by the second week. Magnetic resonance imaging 4 weeks after diagnosis revealed near-complete resolution of the extradural mass, followed by gradual improvement in the posterior tibial somatosensory evoked potentials. Transfusion therapy may be diagnostically and therapeutically useful in spinal cord compression secondary to extramedullary hematopoiesis, obviating the need for surgery or radiotherapy.

Blood Transfusion↗