27 research outputs found
Heat-stable enterotoxin receptor/guanylyl cyclase C is an oligomer consisting of functionally distinct subunits, which are non-covalently linked in the intestine
Guanylyl cyclase (GC) C is a heat-stable enterotoxin (STa) receptor with a
monomeric M(r) of approximately 140,000. We calculated from its
hydrodynamic parameters that an active GC-C complex has a M(r) of 393,000,
suggesting that GC-C is a trimer under native conditions. Both trimeric
and dimeric GC-C complexes were detected by 125I-STa binding and
SDS-polyacrylamide gel electrophoresis under non-reducing conditions. The
GC activity and STa binding from intestinal brush border membranes
comigrated in gel filtration and velocity sedimentation with recombinant
GC-C. However, 125I-STa cross-linking demonstrated that STa receptors with
molecular masses of 52 and 74 kDa are non-covalently attached to GC in the
intestine. Radiation inactivation revealed different functional sizes for
basal GC activity, STa-stimulated GC activity, and STa binding (59,
210-240, and 32-52 kDa, respectively). At low radiation doses, basal GC
activity was stimulated, suggesting that GC-C is inhibited by a relatively
large, probably internal structure. These results suggest that STa may
activate GC-C by promoting monomer-monomer interaction (internal
"dimerization") within a homotrimeric GC-C complex, and that GC-C is
proteolytically modified in the brush border membrane but retains its
function
Functional molecular mass of rat hepatic lipase in liver, adrenal gland and ovary is different
Lipoprotein lipase (LPL) is functionally active only as a dimer. It is
also generally assumed that the highly homologous hepatic lipase functions
as a dimer, but no clear evidence has been presented. A hepatic
lipase-like activity, also indicated as L-type lipase, is present in
adrenal and ovary tissues. This enzyme is thought to originate from the
liver and to be identical to hepatic lipase. We determined the functional
molecular mass of hepatic lipase in rat liver, adrenal gland and ovary by
radiation inactivation, a method for determining the functional size of a
protein without the need of prior purification. Samples were exposed to
ionizing radiation at -135 degrees C. Hepatic lipase activity in liver
homogenate showed a single exponential decay. The functional molecular
mass was calculated to be 63 +/- 10 kDa. Hepatic lipase activity in
adrenal homogenate was found to have a functional molecular mass of 117
+/- 16 kDa. The functional molecular masses of the lipases partially
purified from rat liver perfusate, adrenal homogenate or ovarian
homogenate showed the same pattern, a target mass for the liver enzyme of
56 +/- 6 kDa and a target mass of 117 +/- 14 kDa for the enzyme from
adrenal gland or ovary. In Western blot analysis the mass of the
structural units of hepatic lipase in liver was 57 kDa and in adrenal and
ovary tissue 51 kDa. We conclude that the functional unit of hepatic
lipase in the liver is a monomer. The enzyme in adrenal gland and ovary is
different from the liver and the functional unit may be a dimer
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Influences of non-singular stresses on plane-stress near-tip fields for pressure-sensitive materials and applications to transformation toughened ceramics
In this paper, we investigate the effects of the non-singular stress ( T stress) on the mode I near-tip fields for elastic perfectly plastic pressure-sensitive materials under plane-stress and small-scale yielding conditions. The T stress is the normal stress parallel to the crack faces. The yield criterion for pressure-sensitive materials is described by a linear combination of the effective stress and the hydrostatic stress. Plastic dilatancy is introduced by the normality flow rule. The results of our finite element computations based on a two-parameter boundary layer formulation show that the total angular span of the plastic sectors of the near-tip fields increases with increasing T stress for materials with moderately large pressure sensitivity. The T stress also has significant effects on the sizes and shapes of the plastic zones. The height of the plastic zone increases substantially as the T stress increases, especially for materials with large pressure sensitivity. When the plastic strains are considered to be finite as for transformation toughened ceramics, the results of our finite element computations indicate that the phase transformation zones for strong transformation ceramics with large pressure sensitivity can be approximated by those for elastic-plastic materials with no limit on plastic strains. When the T stress and the stress intensity factor K are prescribed in the two-parameter boundary layer formulation to simulate the crack-tip constraint condition for a single-edge notch bend specimen of zirconia ceramics, our finite element computation shows a spear shape of the phase transformation zone which agrees well with the corresponding experimental observation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42782/1/10704_2004_Article_BF00018779.pd
Revision of (sub)nanosecond pulser for IRI Van de Graaff electron accelerator aided by field propagation calculations
The shorted air line stub used for subnanosecond pulsing of the grounded-grid cathode gun structure of the IRI 3 MV Van de Graaff electron accelerator is revised. Three-dimensional high-frequency field propagation calculations provide better insight into the performance of different geometrical shapes. Effects on rise- and decay time, and ringing on the output pulses are considered. Practical possibilities for improvement are discussed. Comparison with sampling measurements on several device modifications confirms the reliability of the calculations. The calculation method is subsequently used as design aid for the construction of a "1 ns" device using a quartz loaded shorted stub to fit into the geometry of the existing variable pulse length unit. Capabilities for short pulsing of the accelerator are improved and extended by application of the results obtained
Revision of (sub)nanosecond pulser for IRI Van de Graaff electron accelerator aided by field propagation calculations
The shorted air line stub used for subnanosecond pulsing of the grounded-grid cathode gun structure of the IRI 3 MV Van de Graaff electron accelerator is revised. Three-dimensional high-frequency field propagation calculations provide better insight into the performance of different geometrical shapes. Effects on rise- and decay time, and ringing on the output pulses are considered. Practical possibilities for improvement are discussed. Comparison with sampling measurements on several device modifications confirms the reliability of the calculations. The calculation method is subsequently used as design aid for the construction of a "1 ns" device using a quartz loaded shorted stub to fit into the geometry of the existing variable pulse length unit. Capabilities for short pulsing of the accelerator are improved and extended by application of the results obtained