Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q86TM3 (cage)
 29,987 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several models for the action of alpha amylase have been proposed to account for the nonrandom distribution of oligosaccharides in the amylase digests of polysaccharides. The preferred-attack model attempts to account for the nonrandom distribution by assuming that the probability for bond cleavage depends upon the position of the bond in the chain. The repetitive, or multiple-attack, model suggests that the nonrandom distribution of oligosaccharides arises because an amylase can form a cage-like complex with a substrate and attack it several times during a single encounter. The multiple-enzyme or dual-site model suggests that the nonrandom yield of oligosaccharides arises from the combined action of exo- and endo-enzymes. The effects of pH, inhibitors, and substrate chain-length on enzyme action have been studied in several laboratories to determine which of the three action-patterns best describes the action of alpha amylase. The influence of these variables on product distributions or enzyme action-patterns are mathematically modeled in the Appendix. The experimental data on porcine-pancreatic alpha amylase are discussed in the light of the derivations.
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PMID:Models for depolymerizing enzymes: criteria for discrimination of models. 0 53

Structures resembling nuclei are released when HeLa cells are lysed in a detergent and 2 M salt. These nucleoids, which lack any organized membrane structure, contain all the nuclear DNA packaged within a cage of RNA and protein. Their DNA is supercoiled so that the linear DNA must remain unbroken and looped during lysis. Following digestion with the restriction endonuclease, EcoRI, cages and associated DNA were filtered free of unattached DNA. Pulse-labelled (i.e. newly synthesized) DNA remains preferentially associated with the cages. This association has been confirmed by autoradiography. When nucleoids are prepared for electron microscopy by the Kleinschmidt procedure the DNA spills out to form a skirt around the flattened cage. Labelling, which is restricted to the region of the cage after short pulses, extends out into the skirt as the labelling time increases. A model, based on the premise that replication takes place at the nuclear cage, is presented in the Appendix. The results of the biochemical experiments and electron microscopy both indicate that the average size of the unit of replication is approximately 2 micrometer. This is about one-quarter the size of the average structural unit - the loop. Therefore sequences in the loop must become attached to the nuclear cage prior to the initiation of DNA synthesis.
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PMID:DNA is replicated at the nuclear cage. 722 13

An analytic solution is given for the electromagnetic problem of a lossy dielectric cylinder of infinite length, irradiated by a circularly polarized radiofrequency (RF) magnetic field; the NMR-active components of the field inside the cylinder are projected out by transforming the RF Hamiltonian to the rotating frame and retaining only those terms independent of time; it is noted that the resulting cartesian field components are required to be real. The squared magnitude of the NMR-active fields are then used to calculate the gradient-recalled images of the cylinder, for small tip angles of the magnetization; and the result is shown to predict almost quantitatively the intensity patterns of experimental proton images at 3.0 and 4.0T, in a cylindrical phantom of radius 9.25cm, filled with 0.05M aqueous NaCl. In particular, the artifactual brightening at the center of the recorded image is convincingly reproduced in a simulation, whose underlying model excludes wave propagation along the direction of the cylinder axis. Formation of the artifact is explained in terms of the focussing of the RF magnetic field at the center of the cylinder, as illustrated by contour plots showing the time evolution of the rotating flux. An extended electromagnetic model--having the dielectric cylinder enclosed in a long, shielded volume resonator (e.g., of bird cage type)--is then sketched. The mathematical details appear in Appendix A; and the simulated images are shown to be virtually indistinguishable from those of the simpler original model. The theory of the Q, or quality factor, of the dielectric cylinder--considered itself as a resonant object--is developed for the enclosed cylinder model, where flux containment by the shield permits an unambiguous treatment of both the stored energy and the radiative losses. This is extended to treat the Q of a lossy dielectric sphere without shielding. Further plots of flux contours are given for the sphere, excited at 208 MHz with a uniform circularly polarized field, as well as by a surface coil, and for the enclosed cylinder in the range 140-160 MHz. It is then argued that the center brightening artifacts in magnetic resonance images are due to the underdamped dielectric resonance of the sample, i.e., at Q >0.5, while the overdamped condition, Q < 0.5, leads to exclusion of flux from the center, i.e., to the classic skin effect. The term "dielectric resonance" is shown to require careful interpretation for mixed-mode excitation, such as occurs with a surface coil. An extended reciprocity formula for NMR reception, valid for an arbitrary electromagnetic Green's function, is also given in Appendix B.
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PMID:Image brightening in samples of high dielectric constant. 1498 93