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151.
Sehested J Diernaes L Møller PD Skadhauge E 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》1999,123(4):908-368
The unidirectional transport and metabolism of 14C-labeled acetate, propionate and butyrate across the isolated bovine rumen epithelium was measured in vitro by the Ussing chamber technique. There was a significant, but relatively small, net secretion of acetate and propionate, and a large and significant net absorption of butyrate. The results demonstrate that the mucosal-serosal (MS) pathway for short-chain fatty acids (SCFA) is different from the serosal-mucosal (SM) pathway, and that butyrate is treated differently from acetate and propionate by the epithelium. The results support that the main route for epithelial SCFA transport is transcellular. The correlation between SCFA lipophility and the flux rate was positive but weak at both pH 7.3 and 6.0. Decreasing pH increased all SCFA fluxes significantly, but not proportionally to the increase of protonized SCFA in the bathing solution. There was a significant and apparently non-competitive interaction between the transport of acetate, propionate and butyrate. It seems that mediated transport mechanisms must be involved in epithelial SCFA transport in the bovine rumen, but the data do not exclude that passive diffusion could account for a significant part of the flux. The metabolism of SCFA in the Ussing chamber system was considerable, and there was a clear preference for excretion of CO2 from this metabolism to the mucosal side, while side preference for non-CO2 metabolite excretion was not studied. Of the propionate and butyrate transported in the MS direction, 78 and 95% was metabolised, while only 37 and 38% was metabolised in the SM direction (acetate metabolism could not be measured). There was, however, no simple relation between the degree of metabolism and the transport rate or the transport asymmetry of the SCFA. 相似文献
152.
153.
Summary The role of serum albumin in the transport of orally administered L-tryptophan (Trp) into rat tissues was examined using analbuminemic and Sprague-Dawley (SD) rats with and without a-methyl-DL-tryptophan (AMT)-induced Trp depletion. Trp was orally administered to rats 16h after AMT or 0.85% NaCl administration, when liver tryptophan 2,3-dioxygenase and protein synthetic activities in AMT-treated rats were similar to those of 0.85% NaCl-treated rats. After oral Trp administration, regardless of the presence or absence of Trp depletion, free serum Trp concentrations were similar in the analbuminemic and SD rats, while total serum Trp concentrations were lower in analbuminemic rats than in SD rats. Although liver, brain, and muscle Trp concentrations after oral Trp administration under Trp depletion were lower in analbuminemic rats than in SD rats, the ratio of the liver Trp concentration in analbuminemic rats to that in SD rats was smaller than that of the brain or muscle Trp concentration. These results suggest that variations in serum albumin levels could affect the transport of orally administered Trp into the liver of rats with Trp depletion. 相似文献
154.
Methylphenidate (MPD) was found to inhibit competitively the striatal dopamine transporter (DAT) and bind at sites on the DAT in common with both cocaine (a non-substrate site ligand) and amphetamine (a substrate site ligand). Some methylphenidate analogues modified on the aromatic ring and/or at the nitrogen were tested to determine whether the profile of inhibition could be altered. None was found to stimulate the release of dopamine in the time frame (< or = 60 s) of the experiments conducted, and each of the analogues tested was found to noncompetitively inhibit the transport of dopamine. It was found that halogenating the aromatic ring with chlorine (threo-3,4-dichloromethylphenidate hydrochloride; compound 1) increased the affinity of MPD to inhibit the transport of dopamine. A derivative of MPD with simultaneous, single methyl group substitutions on the phenyl ring and at the nitrogen (threo-N-methyl-4-methylphenidate hydrochloride; compound 2) bound at a site in common with MPD. A benzyl group positioned at the nitrogen (threo-N-benzylmethylphenidate hydrochloride; compound 3) imparted properties to the inhibitor in which binding at substrate and non-substrate sites could be distinguished. This analogue bound at a mutually interacting site with that of methylphenidate and had a K(int) value of 4.29 microM. Furthermore, the N-substituted analogues (compounds 2 and 3), although clearly inhibitors of dopamine transport, were found to attenuate dramatically the inhibition of dopamine transport by amphetamine, suggesting that the development of an antagonist for substrate analogue drugs of abuse may be possible. 相似文献
155.
156.
The challenges of moving chemicals within and out of cells: insights into the transport of plant natural products 总被引:9,自引:0,他引:9
Grotewold E 《Planta》2004,219(5):906-909
157.
Deigweiher K Drell TL Prutsch A Scheidig AJ Lübben M 《Journal of bioenergetics and biomembranes》2004,36(1):151-159
The P-type CPX-ATPases are responsible for the transport of heavy metal ions in archaea, bacteria, and eukaryotes. We have chosen one of the two CPX-ATPases of the thermophile Sulfolobus solfataricus, CopB (= SSO2896) for the investigation of the molecular mechanism of this integral membrane protein. We recombinately expressed three different soluble domains of this protein (named CopB-A, CopB-B, and CopB-C) in Escherichia coli and purified them to homogeneity. 3D crystals of CopB-B, the 29 kDa catalytic ATP binding/phosphorylation domain were produced, which diffracted to a resolution of 2.2 A. CopB-B has heavy metal stimulated phosphatase activity, which was half maximal in the presence of 80 microM Cu2+. The protein forms a phosphorylated intermediate with the substrate gamma-(32P)-ATP. No specific activation of the polypeptide was observed, when CopB-B phosphatase activity was tested in the presence of the purified CopB-C and CopB-A proteins, which provide the cation binding and the phosphatase domains. We conclude that CopB is a putatively copper translocating ATPase, in which structural elements integrally located in the membrane are required for full, coordinated activation of the catalytic ATP binding domain. 相似文献
158.
Satoh M Kubo T Nishizawa S Estiati A Itchoda N Mikami T 《Molecular genetics and genomics : MGG》2004,272(3):247-256
The complete nucleotide sequence (501,020 bp) of the mitochondrial genome from cytoplasmic male-sterile (CMS) sugar beet was determined. This enabled us to compare the sequence with that previously published for the mitochondrial genome of normal, male-fertile sugar beet. The comparison revealed that the two genomes have the same complement of genes of known function. The rRNA and tRNA genes encoded in the CMS mitochondrial genome share 100% sequence identity with their respective counterparts in the normal genome. We found a total of 24 single nucleotide substitutions in 11 protein genes encoded by the CMS mitochondrial genome. However, none of these seems to be responsible for male sterility. In addition, several other ORFs were found to be actively transcribed in sugar beet mitochondria. Among these, Norf246 was observed to be present in the normal mitochondrial genome but absent from the CMS genome. However, it seems unlikely that the loss of Norf246 is causally related to the expression of CMS, because previous studies on mitochondrial translation products failed to detect the product of this ORF. Conversely, the CMS genome contains four transcribed ORFs (Satp6presequence, Scox2-2 , Sorf324 and Sorf119) which are missing from the normal genome. These ORFs, which are potential candidates for CMS genes, were shown to be generated by mitochondrial genome rearrangements.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by R. Hagemann 相似文献
159.
Zhang Z Feige JN Chang AB Anderson IJ Brodianski VM Vitreschak AG Gelfand MS Saier MH 《Archives of microbiology》2003,180(2):88-100
An ABC-type transporter in Escherichia coli that transports both l- and d-methionine, but not other natural amino acids, was identified. This system is the first functionally characterized member of a novel family of bacterial permeases within the ABC superfamily. This family was designated the methionine uptake transporter (MUT) family (TC #3.A.1.23). The proteins that comprise the transporters of this family were analyzed phylogenetically, revealing the probable existence of several sequence-divergent primordial paralogues, no more than two of which have been transmitted to any currently sequenced organism. In addition, MetJ, the pleiotropic methionine repressor protein, was shown to negatively control expression of the operon encoding the ABC-type methionine uptake system. The identification of MetJ binding sites (in gram-negative bacteria) or S-boxes (in gram-positive bacteria) in the promoter regions of several MUT transporter-encoding operons suggests that many MUT family members transport organic sulfur compounds. Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material. 相似文献
160.
Membrane glycine transport proteins 总被引:1,自引:1,他引:0
Tunnicliff G 《Journal of biomedical science》2003,10(1):30-36
Structurally, the simplest amino acid is glycine, and it has a number of important yet distinct functions in the body. This review focuses on the different transport systems and the associated carrier proteins for glycine that are responsible for its movement across biological membranes. Transport proteins in the class GLYT appear to be the most specific for glycine. However, the B0+ system also carries significant amounts of glycine. Other amino acid transport systems capable of carrying small amounts of glycine are ASC, asc and system L. In addition, an ATP-dependent transport process exists that takes up glycine into synaptic vesicles at nerve endings. This is known as the vesicular inhibitory amino acid transporter since, in addition to glycine, it can transport possibly two other inhibitory neurotransmitters. 相似文献