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Biomedical subjects

R Feder

Publications and source records attributed to R Feder.

53 records · Page 3Linked to original sources
PubMed1981

Improved detail in biological soft X-ray microscopy: study of blood platelets.

Improved image quality in soft x-ray contact microscopy can be obtained by examining the resist with transmission rather than scanning electron microscopy. Application of the new technique to air-dried preparations of human blood platelets reveals structures not visible in the same cells with transmission electron microscopy or when the resist is examined by scanning electron microscopy. As seen by the new technique, platelet pseudopods contain a central structure connected to a network in the platelet and dense bodies exhibit a lamellar structure.

Blood Platelets↗
PubMed1980

Imaging unstained proteoglycan aggregates by soft x-ray contact microscopy.

Soft X-ray contact microscopy is a relatively new form of ultrastructural imaging, having better than 6 nm resolution and being uniquely well suited for the examination of fragile, unstained biological specimens. The biological specimen placed on a layer of photoresist and exposed to soft X-rays (1-10 nm lambda) of a specific wavelength or broad band. After X-ray exposure, the specimen is removed from the photoresist and the latter chemically developed. When the developed replica is examined by high resolution scanning electron microscopy, the fine structure of the original biological specimen is faithfully reproduced. Since the soft X-ray replica is initially formed due to the differential absorption of the incident X-rays by the biological specimen, the resultant contact replica also reveals information about the elemental composition of the sample. This paper presents our application of this new technique for the study of the proteoglycans, the complex polyanionic macromolecules comprising the gel phase in the matrix of mammalian cartilage.

Animals↗
PubMed1980

Soft x-ray lithographic studies of interphase chromosomes.

Soft x-ray absorption lithograph patterns of purified interphase human nuclei and chromosome arrays, imaged on PMMA resists, were examined by scanning EM. The patterns obtained were compared to those utilizing more conventional sources, including transmission EM, scanning EM, high voltage EM, and various light microscopic techniques. The x-ray resist images revealed orderly arrays of absorption profiles in the 3-dimensional specimen with both mild and more extensive developments of the resist. Dense chromatin at the edge of interphase nuclei revealed aligned periodic peaks on the order of 2200 A diameter, with substructure. The periodicity and alignment of interphase chromosomes were entirely consistent with birefringent data on nuclei indicating a high degree of 3-dimensional order. This degree of 3-dimensional order was observed in nuclei containing essentially DNA and histones with only very few other minor (probably structural) proteins. Sonication and nuclease treatment to disperse interphase chromosomes revealed similar absorption periodicities in individual chromosome fibers. Analysis of x-ray absorption profiles thus appears to offer significant new insights into the ordered structure of these defined biological specimens.

Cell Cycle↗
PubMed1980

Ultrastructural and elemental imaging of biological specimens by soft X-ray contact microscopy.

Soft X-ray contact microscopy offers a means of visualizing unstained as well as stained biological materials at better than 6 nm resolution. Unlike light and transmission electron microscopy, which rely on stains to increase specimen contrast, soft X-ray imaging is dependent upon the differential absorption of incident soft (1-10nm wavelength) X-rays by the endogenous elements within the specimen. The advantages of using soft X-rays for imaging are: 1) reduced specimen damage during exposure; 2) ability to image hydrated specimens at atmospheric pressure; 3) ability to image specimens ranging in thickness from less than 40 nm to as much as 10 microns; and 4) ability to map the elemental composition of the specimen through observation of the differential absorption of properly chosen incident x-ray wave lengths. This paper explains the principles of the image formation and demonstrates the use of soft X-ray contact microscopy with biological samples which could not readily be imaged in their natural form using conventional electron microscopy methods.

Animals↗
PubMed1979

High resolution microchemical analysis using soft X-ray lithographic techniques.

High resolution x-ray lithographic studies of cells from chick embryo hearts dried by the CO2 critical point method have been made with soft x-ray radiation of different wavelengths. A marked difference in the relief replica in polymethyl methacrylate (PMMA) resulting from the differential absorption by the dried cells of carbon K alpha radiation at 4.48 nm and broad band synchrotron radiation (SR) with lambda is greater than 1.5 nm demonstrates the potential usefulness of the technique in making high resolution (approximately or equal to 10 nm) chemical identification of the constitutents which make up the various parts of the cell.

Animals↗
PubMed1977

High-resolution soft x-ray microscopy.

X-ray micrographs of biological materials have been obtained with a resolution better than 100 angstroms by using x-ray resist as the recording medium. A high-resolution scanning electron microscope with a short-focal-length final lens, operating in the "low-loss" mode, is used to make the smallest features in the x-ray replica visible.

Animals↗
PubMed1977

Transmission microscropy of unmodified biological materials: comparative radiation dosages with electrons and ultrasoft x-ray photons.

The minimum radiation dosage in a specimen consistent with transmission microscopy at resolution d and specimen thickness t is calculated for model specimens resembling biological materials in their natural state. The calculations cover 10(4)-10(7) eV electrons and 1.3-90 A photons in a number of microscopy modes. The results indicate that over a considerable part of the (t,d)-plane transmission microscopy on such specimens can be carried out at lower dosage with photons than with electrons. Estimates of the maximum resolutions obtainable with electrons and photons, consistent with structural survival of the specimen, are obtained, as are data on optimal operating conditions for microscopy with the two particles.

Air↗
PubMed1976

X-ray microscopy of biological objects with carbon kappa and with synchrotron radiation.

X-ray micrographs of biological objects have been obtained with a resolution better than 1000 angstroms by using poly(methyl methacrylate) x-ray resist and carbon Kalpha or synchrotron radiation. Synchrotron radiation allows short exposure times; storage rings especially designed as radiation sources and improved x-ray resists would make exposure times under 1 second possible.

Eukaryota↗
PubMedDate not supplied

Primary structure and genomic organization of the histidine-rich protein of the malaria parasite Plasmodium lophurae.

The nucleotide sequence of a complete genomic clone for the histidine-rich protein of Plasmodium lophurae has been determined. The deduced amino acid sequence of the mature protein shows numerous tandemly repeated units preceded by a signal and a pro peptide. The gene is interrupted by an intron with a separate exon coding for the signal peptide. The signal peptide-encoding exon detects multiple cross-hybridizing sequences in the parasite genome.

Amino Acid Sequence↗