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1.
Hiroyuki Kozu Isao Kobayashi Mitsutoshi Nakajima Kunihiko Uemura Seigo Sato Sosaku Ichikawa 《Food biophysics》2010,5(4):330-336
This paper uses computational fluid dynamics to simulate and analyze intragastric fluid motions induced by human peristalsis.
We created a two-dimensional computational domain of the distal stomach where peristalsis occurs. The motion of the gastric
walls induced by an antral contraction wave (ACW) on the wall of the computational domain was well simulated using a function
defined in this study. Retropulsive flow caused by ACW was observed near the occluded region, reaching its highest velocity
of approximately 12 mm/s in the narrowest region. The viscosity of the model gastric contents applied in this study hardly
affected the highest velocity, but greatly affected the velocity profile in the computational domain. The shear rate due to
gastric fluid motion was calculated using the numerical output data. The shear rate reached relatively high values of approximately
20 s−1 in the most occluded region. The shear rate profile was almost independent of the fluid viscosity. We also simulated mass
transfer of a gastric digestive enzyme (pepsin) in model gastric content when peristalsis occurs on the gastric walls. The
visualized simulation results suggest that gastric peristalsis is capable of efficiently mixing pepsin secreted from the gastric
walls with an intragastric fluid. 相似文献
2.
Cloning and sequencing of Schizosaccharomyces pombe DNA topoisomerase I gene, and effect of gene disruption. 总被引:18,自引:7,他引:11
We cloned the structural gene topl+ for Schizosaccharomyces pombe DNA topoisomerase I (topo I) by hybridization. An eight-fold increase of topo I relaxing activity was obtained in S. pombe cells transformed with multicopy plasmid with topl+ insert. Nucleotide sequence determination showed a hypothetical coding frame interrupted by two short introns, encoding a 812 residue polypeptide (M.W. 94,000), 43 residues longer than and 47% homologous to Saccharomyces cerevisiae topo I. We show that the topl (null) strain made by gene disruption is viable, although its generation time is 20% longer than that of wild type. The topl locus is mapped in the long arm of chromosome II, using the Leu+ marker integrated with the cloned topl+ sequence. We constructed a double mutant topl (null) top2 (ts) and found its defective phenotype similar to that of previously obtained topl (heat sensitive) top2 (ts). The other double mutant topl (null) top2 (cs), however, was lethal. Our results suggest that topl+ gene of S. pombe is dispensable only if topo II activity is abundant. 相似文献
3.
4.
Calyculin A and okadaic acid: inhibitors of protein phosphatase activity 总被引:44,自引:0,他引:44
H Ishihara B L Martin D L Brautigan H Karaki H Ozaki Y Kato N Fusetani S Watabe K Hashimoto D Uemura 《Biochemical and biophysical research communications》1989,159(3):871-877
Calyculin A and okadaic acid induce contraction in smooth muscle fibers. Okadaic acid is an inhibitor of phosphatase activity and the aims of this study were to determine if calyculin A also inhibits phosphatase and to screen effects of both compounds on various phosphatases. Neither compound inhibited acid or alkaline phosphatases, nor the phosphotyrosine protein phosphatase. Both compounds were potent inhibitors of the catalytic subunit of type-2A phosphatase, with IC50 values of 0.5 to 1 nM. With the catalytic subunit of protein phosphatase type-1, calyculin A was a more effective inhibitor than okadaic acid, IC50 values for calyculin A were about 2 nM and for okadaic acid between 60 and 500 nM. The endogenous phosphatase of smooth muscle myosin B was inhibited by both compounds with IC50 values of 0.3 to 0.7 nM and 15 to 70 nM, for calyculin A and okadaic acid, respectively. The partially purified catalytic subunit from myosin B had IC50 values of 0.7 and 200 nM for calyculin A and okadaic acid, respectively. The pattern of inhibition for the phosphatase in myosin B therefore is similar to that of the type-1 enzyme. 相似文献
5.
H Ariyoshi E Shiba J Kambayashi M Sakon T Tsujinaka Y Uemura T Mori 《Biochemistry international》1991,23(6):1019-1033
Calpeptin (a cell permeable synthetic peptide calpain inhibitor) inhibited the generation of thromboxane B2 (TxB2) by the direct inhibition on Tx synthetase in platelets at the concentrations more than 30 microM. Calpeptin, its analogues and E-64d (EST) were further examined with regard to cell permiability and inhibitory spectra. Among all compounds, only calpeptin inhibited the degradation of substrate proteins of calpain with negligible effect on TxB2 generation in intact platelets at the concentrations less than 30 microM. These concentrations of calpeptin did not inhibit the platelet aggregation, the elevation of [Ca2+], nor the formation of inositol 1,4,5-trisphosphate (IP3) in thrombin or collagen activated platelets. These results indicate that calpain dose not participate in the process of platelet activation induced by thrombin or collagen. 相似文献
6.
Escherichia coli supH suppressor: temperature-sensitive missense suppression caused by an anticodon change in tRNASer2. 总被引:12,自引:5,他引:7 下载免费PDF全文
S Thorbjarnardttir H Uemura T Dingermann T Rafnar S Thorsteinsdttir D Sll G Eggertsson 《Journal of bacteriology》1985,161(1):207-211
We describe the cloning and the DNA sequence of the Escherichia coli supH missense suppressor and of the supD60(Am) suppressor genes. supH is a mutant form of serU which codes for tRNASer2. The supH coding sequence differs from the wild-type sequence by a single nucleotide change which corresponds to the middle position of the anticodon. The CGA anticodon of wild-type tRNA and CUA anticodon of supD tRNA is changed to CAA in supH tRNA, which is expected to recognize the UUG leucine codon. We propose that the supH suppressor causes the insertion of serine in response to this codon. The temperature sensitivity caused by supH may be due to a conformation of the CAA anticodon in the supH tRNASer that is slightly different than that in the corresponding tRNALeu species. 相似文献
7.
Isolation and Characterization of Tonoplast from Chilling-Sensitive Etiolated Seedlings of Vigna radiata L 总被引:2,自引:0,他引:2 下载免费PDF全文
Tonoplasts were isolated in a high purity from etiolated young seedlings of Vigna radiata L. (mung bean) utilizing a sucrose density gradient system. The excised hypocotyls were homogenized in a sorbitol-buffer system and the 3,600 to 156,000g pellets obtained after the differential centrifugations were suspended in a sorbitol medium and loaded on a linear sucrose density gradient. After centrifugation at 89,000g for 2 hours, tonoplasts were banded at the sample load/sucrose interface. Assessed by electron microscopy and marker enzymes, the purity and the quantity were found to be sufficient for biochemical and biophysical analyses. The tonoplasts were associated with NO3−-sensitive and vana-date-insensitive ATPase. The tonoplast ATPase was stimulated by proton ionophores such as carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone and gramicidin D, suggesting a proton-pumping enzyme. In the presence of ATP and Mg2+, a proton gradient was formed in the isolated tonoplast vesicles as assessed by fluorescence quenching of quinacrine. The tonoplasts contained several kinds of mannosylated or glycosylated glycoproteins and a major protein (65 kilodaltons) which was unique to the membranes. 相似文献
8.
9.
Na+-dependent I- transport and I- counterflow were studied using phospholipid vesicles (P-vesicles) made of porcine thyroid plasma membranes and soybean phospholipid by sonication. 1) I- uptake by P-vesicles incubated in the presence of external Na+ was higher than that by P-vesicles incubated in choline+ instead of Na+. The vesicles exhibited Na+-dependent I- uptake. When P-vesicles were internally loaded with I- prior to incubation in Na+, a further increase in Na+-dependent I- uptake was observed, although the concentration of internal I- was very much higher than that outside. In the absence of external Na+, I- uptake by P-vesicles preloaded with I- was comparable to baseline uptake. 2) Na+-dependent I- uptake by P-vesicles not loaded with I- and enhanced Na+-dependent I- uptake by P-vesicles preloaded with I- were both inhibited by either of SCN- and ClO4- added outside the vesicles. 3) When P-vesicles were loaded with SCN- instead of I- and incubated in Na+, I- uptake by these vesicles was also higher than baseline Na+-dependent I- uptake. However, a ClO4- load did not result in an increase in I- uptake. These results indicate that Na+-dependent I- transport including Na+-dependent I- counterflow is specifically mediated by the thyroid I- carrier. SCN- - I- counterflow in addition to I- - I- counterflow occurs dependently on Na+, but ClO4- - I- counterflow does not. 相似文献
10.
The thin-layer-chromatography immunostaining procedure was applied to human erythrocyte glycolipids using monoclonal anti-i and anti-I antibodies which are directed against epitopes on linear and branched carbohydrate chains of the neolacto (poly-N-acetyl-lactosamine) series. An examination of native and mild-acid-treated glycolipids from normal adult (Iadul t antigen type), neonatal (icord) , and I-antigen-deficient adult (iadult) erythrocytes enabled certain structural inferences to be made as follows: (a) cells of both I and i phenotypes contain a multiplicity of glycolipids of the neolacto series whose backbones consist of 8 or more sugar residues; (b) the octasaccharide backbones are predominantly linear in cells of i phenotype and branched in those of I type; and (c) more complex glycolipids having decasaccharide and larger backbones with both linear and branched sequences occur in erythrocytes of both phenotypes, 0 相似文献