59 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
Functional molecular mass of rat hepatic lipase in liver, adrenal gland and ovary is different
Revision of (sub)nanosecond pulser for IRI Van de Graaff electron accelerator aided by field propagation calculations
Pulse radiolysis with (sub) nanosecond time resolution using a 3MV electron accelerator
Applied Science
Fluorescent solvent excited states from hole-electron recombination in cis- and trans-decalin irradiated with high energy electrons
Single- and doubkle-strand breaks in DNA of the bacteriophage T4 corelated with biological inactivation of the phage after irradiation
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