PubMed Health⌕ Search

Biomedical subjects

J F Hainfeld

Publications and source records attributed to J F Hainfeld.

78 records · Page 5Linked to original sources
PubMed1983

Epidermal keratin filaments assembled in vitro have masses-per-unit-length that scale according to average subunit mass: structural basis for homologous packing of subunits in intermediate filaments.

We have used scanning transmission electron microscopy to elucidate the question of how intermediate filament (IF) subunits of widely differing mass can all form morphologically similar IF. From scanning transmission electron micrographs, the distributions of mass were determined for three types of epidermal keratin IF reassembled in vitro from mixtures of subunits with substantially different masses, viz., "light" and "heavy" human keratins with [Mr] = 50,000 and 56,000, respectively, and mouse keratins of [Mr] = 63,000. Their principal assembly products were found to average 22, 25, and 29 kdalton/nm, respectively. These densities, which correspond to immature "minimal form" IF (Steven, A. C., J. Wall, J. Hainfeld, and P. M. Steinert, 1982, Proc. Natl. Acad. Sci. USA., 79:3101-3105), are directly proportional to the average subunit masses. The human keratin IF (but not those of mouse) also contained minor amounts (15-20%) of more massive polymers averaging 33 and 35 kdalton/nm, respectively, which probably represent mature IF. Taken together with earlier results on IF of other subclasses, these results indicate that the average linear density of IF scales according to the average mass of their constituent subunits, both for "minimal form" and for mature IF. As underlying mechanism for this homology, we propose that the fundamental building-blocks of all these IF contain a common structural element whose packing within the various IF is likewise conserved and which specifies the overall structure. The variable amounts of mass in the nonconserved moieties account for the observed proportionality. This scheme fits with amino acid sequence data for several IF subunits that have revealed, as a likely candidate for the common element, an essentially conserved alpha-helical domain, contrasting with the highly variable sequences of their non-alpha-helical terminal domains.

Animals↗
PubMed1982

A small computer system for micrograph analysis.

A small computer system is described that makes use of video graphics to interactively analyze electron micrographs. The advent of relatively inexpensive digital frame buffers (digital memory that holds one TV frame) permits an image of at least 512X512 pixel resolution to be displayed and rapidly changed in contrast, brightness, and color. These devices can also perform pan (picture movement), zoom and marking of objects of interest with circles, vectors and alphanumerics. These features have suddenly made it possible to quantitatively analyze micrographs in an efficient and interactive way. A minimal system is described here to implement the application of this equipment to measure molecular weights of individual proteins (or mass per unit length measurements) and to perform several image enhancement processes such as background gradient removal and contouring of molecules. This system is a stand-alone microcomputer with disk, video processor and TV set and is simple enough to permit an untrained user to make a statistical study of his micrographs after only a few minutes of instruction.

Apoferritins↗
PubMed1977

The sub-membrane reticulum of the human erythrocyte: a scanning electron microscope study.

A web-like reticulum underlying the human erythrocyte membrane was studied at a resolution of 5-10 nm by means of scanning electron microscope. The network was visualized in isolated membranes (ghosts) torn open to reveal their interior space and in residues derived from ghosts extracted with Triton X-100. It formed a continuous (rather than patchy) cover over the entire cytoplasmic surface, except where lifted off or torn away. Filaments (5-40 nm in diameter), annular figures (40-60 nm in diameter), and nodes (30-100 nm in diameter) were prominent in different networks. The dimensions of the filaments and the interstices in the reticulum varied with conditions, suggesting that the network has elastic properties. This reticulum is probably related to the erythrocyte membrane proteins spectrin and actin.

Cell Fractionation↗
PubMedDate not supplied

Visualization of a ternary complex of the Escherichia coli Phe-tRNA(Phe) and Tu.GTP from Thermus thermophilus by scanning transmission electron microscopy.

Scanning transmission electron microscopy (STEM) was used to visualize formation of a ternary complex between the T. thermophilus elongation factor (EF) Tu.GTP and the Escherichia coli Phe-tRNA(Phe) labeled with an undecagold (Au11) cluster at minor nucleotide 3-(3-amino-3-carboxypropyl) uridine at position 47. The ternary complex was further characterized by the molecular mass and radius of gyration calculated from the mass distribution within the individual particles. Under conditions used for STEM imaging, the ternary complex is formed between Au11-labeled Phe-tRNA(Phe) and Tu.GTP in a yield up to 25%. The stoichiometry of EF-Tu.GTP to aminoacyl-tRNA (aa-tRNA) in the EF-Tu.GTP.aa-tRNA complex is 1:1, in agreement with the established view of the protein biosynthesis mechanism. The ternary complex is also formed, although to a lower extent, with GTP analogues (GMPPCP and GMPPNP, respectively), but not with Tu.GDP and nonaminoacylated tRNA(Phe) with Tu.GTP.

Escherichia coli↗
PubMedDate not supplied

The covalent structure of factor XIIIa crosslinked fibrinogen fibrils.

When factor XIIIa-mediated crosslinking of fibrin or fibrinogen occurs, reciprocal intermolecular isopeptide bonds form first between paired carboxy terminal gamma chain donor-acceptor sites in outer molecular D domains, resulting in gamma chain dimers. Their location in the fibrin polymer is not certain, but some evidence suggests they are situated at the outermost ends of the D domains of linearly aligned molecules comprising each strand of double-stranded fibrils ("DD-long"). Other experiments indicate that gamma chain bonds are located between D domains in opposing fibril strands ("transverse"). To distinguish between these possible arrangements, we evaluated the ultrastructure of fibrils and fibers found in factor XIIIa-fibrinogen crosslinking mixtures, based on this reasoning: if DD-long bonding occurs, single-stranded fibrils should result, whereas transverse positioning will result in double-stranded fibrils. Fibrils formed in partially cross-linked fibrinogen solutions consisted of two parallel strands, as discerned visually from scanning transmission electron microscopic images and confirmed by mass per unit length fibril measurements. Neighboring fibrinogen D domains in each fibril strand were aligned end-to-end and were in register with a fibrinogen E domain in the opposite strand, creating a half-staggered molecular arrangement with approximately 22.5-nm periodicity corresponding to half the length of fibrinogen. Ribbon-like fibrinogen fibers, like fibrils, displayed 22.5-nm periodicity, as expected from laterally associated double-stranded fibrils with D domains in register. Taken together, these results indicate that carboxy terminal gamma chain bonds are positioned transversely between strands and are represented by thin filamentous structures bridging the D domains of opposing fibril strands--it follows that the same gamma chain crosslink arrangement occurs in fibrin.

Chromatography, Gel↗