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1.
To elucidate T4 metabolism in various cell types of rat retina, 5-monodeiodinating and 5′-monodeiodinating activities were studied in retinal cell layers obtained by selective cytotoxic action of monosodium glutamate on bipolar and ganglion cell layers and by iodoacetate effect on photoreceptor cells. Concomitantly these enzyme activities were studied in C3H/HeN mouse retina genetically deprived of photoreceptor cells. Deiodinase activities were low in rat and mouse retina deprived of photoreceptors. The 5′-monodeiodination rate of T4 was higher than T4 tyrosyl ring deiodination in cell layers examined and the highest values were found in the photoreceptor cells. Data support the hypothesis that phenolic and tyrosyl ring deiodinase activities are present in the photoreceptor cells. Their reciprocal changes may regulate the nuclear function which in turn controls the rhythmical renewal of rod outer segments.  相似文献   

2.
Cultured monkey hepatocarcinoma cells (NCLP-6E) were used to investigate the uptake and metabolism of thyroid hormones. Intracellular accumulation was shown by the failure to acutely release hormone from cells subsequently exposed to serum proteins, and by the metabolic transformation of the hormones to deiodinated products and their sulfates. When hepatocarconoma cell monolayers were studied at hormone concentrations below 10?10 M, neither KCN nor dinitrophenol inhibited uptake. Taken together with previous findings that uptake was neither saturable nor reduced at low temperature, these results indicate that this process was not active transport. Deiodination of both the phenolic and non-phenolic rings, however, was partially inhibited by KCN but not by dinitrophenol. Sulfation of 3,3′-diiodothyronine and 3′-monoiodothyronine was strongly inhibited by both KCN and dinitrophenol.Uptake of the hormones and their metabolites was also measured in suspended hepatocarcinoma cells and compared with the uptake by normal rat hepatocytes, human fibroblasts and human lymphocytes. In these experiments 1 μM triiodothyronine and 0.47 mM dinitrophenol were used to inhibit deiodination and sulfation, respectively. Uptake was similar in all cell types. Accumulation was highest with 3,5,3′-triiodothyronine, intermediate with other compounds having iodines in both rings, lowest with compounds iodinated in only one ring, and absent with iodothronine sulfates. These findings help to explain the relative rates of metabolism of the iodothyronines and their release from the cells.  相似文献   

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Mitochondria isolated from rat heart contained nucleoside diphosphokinase (EC 2.7.4.6) at a specific activity of 30 mIU/mg protein, or about one half of liver mitochondrial activity, 60 mIU/mg. In contrast to liver mitochondria, no stimulation of O2 uptake was observed when 150 μM GDP was added to heart mitochondria respiring in post-ADP State 4, and the transphosphorylation of [γ-32Pi] from ATP into GTP was marginal. However, when heart mitochondria pretreated with oligomycin were solubilized with 0.03% Triton X-100, a five fold increase in the rate of GTP formation was observed. These results show that in heart mitochondria approximately 80% of the nucleoside diphosphokinase activity is localized within the inner compartment.  相似文献   

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In vitro incubations of cytosol proteins from human red blood cells with [125I] labelled L-3,5,3′ triiodothyronine demonstrated the existence of high affinity and limited capacity binding sites for T3. At 4°C, the rate constant of association was 3 × 107 M?1h?1, and the rate constant of dissociation was 9.10?3h?1. The dissociation constant Kd was calculated from these data or measured by Scatchard analysis and found to be between 3 and 7.10?10M. The maximum binding capacity was 1.4 f moles of L-3,5,3′ triiodothyronine per mg cytosol proteins. A close parallel between the biological pontency of the analogs of L-T3 was observed.  相似文献   

8.
Barley embryo 5S rRNA hybridizes efficiently with barley embryo 18S rRNA but not with 26S rRNA. Mouse sarcoma 5S rRNA also selectively hybridizes, to a smaller extent, with mouse sarcoma 18S rRNA. The barley embryo 5S–18S rRNA complex has a sharp melting profile and a “Tm” of ca. 59° in 0.1 M NaCl. The mouse sarcoma 5S–18S rRNA complex has a broader transition breadth and a “Tm” of ca 52°. The conditions used for hybridization lead to very specific reconstitution of the “natural” complex between 5.8S and 26S–28S rRNA since both the invivoandinvitro complexes between 5.8S and 26S–28S rRNA from barley embryos and mouse sarcoma have equally sharp melting profiles and a “Tm” of ca. 52° in 0.1 M NaCl.  相似文献   

9.
Polyphenols of Intsia heartwoods   总被引:2,自引:0,他引:2  
Robinetin is the main polyphenol of the heartwood of Intsia bijuga and is accompanied by smaller amounts of 3,5,4′-tri- and 3,5,3′,4′-tetra-hydroxystilbenes, dihydromyricetin, myricetin and naringenin. The wood contains large amounts of water soluble polymers including leucocyanidin. The stilbenes are absent from the sapwood. Samples of I. bijuga and I. palembanica from several countries revealed differences in composition.  相似文献   

10.
Iodothyronine monodeiodinase activities in homogenates of cultured monkey hepatocarcinoma cells were measured by the deiodination of [3,5-125I]triido-l-thyronine or 3-[3′5′-125I]triido-l-thyronine (phenolic ring-labeled ‘reverse’ triiodothyronine). The assay system utilized a small ion-exchange column (AG50W-X4, 0.9×~1 cm) to measure 125I?. Both deiodinases were destroyed by boiling for 1 min.Maximal nonphenolic ring deiodination was observed at pH 7.9 whereas maximal phenolic ring deiodination was at pH 6.3. Both reactions were enhanced strongly by dithiothreitol (0.1–5 mM), and slightly by 5 mM β-mercaptoethanol. Phenolic ring deiodination was strongly inhibited by 0.1 mM propylthiouracil. Nonphenolic ring deiodination was accelerated by EDTA (1.2 mM) and inhibited by Mg2+ (5 mM). Methylmercaptoimidazol and Mg2+, Ca2+ and Mn2+ (0.1–1.0 mM) had little or no effect on either reaction, but Zn2+ (0.1 mM) strongly inhibited both.Both reactions were inhibited by excess iodothyronine analogues at 10 mM to 10μM, and thyroxine was shown to be a competitive inhibitor in both cases. On the basis of relative affinities and inhibitory effects, it appears that the order of affinity for the phenolic ring deiodinase is 3,3′,5′-triiodo-l-thyronine-(rT3) > l-thyroxine(T4) > 3,4,3′-triido-l-thyronine(T3), whereas for the nonphenolic ring deiodinase the order is T3 > T4 > rT3. Diiodotyrosine did not affect their deiodination.  相似文献   

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The synthesis of 2′-C-methyl-4′-thiocytidine (16) is described. Since the 2′-keto-4′-thiocytidine derivative unexpectedly isomerized to and the methylation of proceeded predominantly from the less hindered α-face to give 7, the desired product 16 was synthesized via the Pummerer reaction of the sulfoxide 14 and N 4 -benzoylcytosine.  相似文献   

14.
To study new natural products, we used ODS (YMC, Kyoto, Japan) and silica gel column chromatography to separate compounds in Cercis chinensis Bunge (Leguminosae). A new stilbene, trans- 3, 5, 3', 4'-tetrahydroxy-4-methylstilbene (1), along with 10 known compounds, namely piceatannol (2), dihydromyricetin (3), catechin (4), dihydrorobinetin (5), menisdaurin (6), lithospermoside (7), teatannin (8), dasycarponin (9), β-sitosterol (10), and daucosterin (11), was isolated from C. chinensis. Their structures were elucidated on the basis of spectroscopic evidence. Compounds 2-6 and 9 were isolated from the genus Cercis Linn. for the first time.  相似文献   

15.
DNA polymerase α1, a subspecies of DNA polymerase α of Ehrlich ascites tumor cells, was associated with a novel RNA polymerase activity and utilized poly(dT) and single-stranded circular fd DNA as a template without added primer in the presence of ribonucleoside triphosphates and a specific stimulating factor. DNA synthesis in the above system was inhibited by the ATP analogue, 2′-deoxy-2′-azidoadenosine 5′-triphosphate more than the DNA synthesis with poly(dT)·oligo(rA) by DNA polymerase α1 and RNA synthesis by mouse RNA polymerases I and II. Kinetic analysis showed that the analogue inhibited DNA polymerase α1 activity on poly(dT) competitively with respect to ATP, suggesting that the analogue inhibited RNA synthesis by the associated RNA polymerase activity.  相似文献   

16.
1. 1. Particulate fractions of costal cartilage from young rats are capable of catalyzing the formation of the first two monosaccharide units of the chondroitin sulfate-protein linkage region.
2. 2. Hormonal imbalance has been shown to influence the activity of the glycosyltransferases responsible for the sequential transfer of xylose and galactose from UDPxylose and UDPgalactose, respectively, in the formation of the linkage region.
3. 3. The activity of xylosyltransferase was found to be decreased in costal cartilage of diabetic, thyroidectomized and hypophysectomized rats, but not in rats injected with either testosterone or hydrocortisone. In the latter two treatment groups, galactosyltransferase activity was decreased only in the group receiving hydrocorsitone.
4. 4. The combined results of this and previous studies suggest that decreased levels of chondroitin sulfate in diabetic, thyroidectomized and hypophysectomized animals are due to interference in the synthesis of the linkage region of the proteoglycan at the xylosyltransferase level whereas hydrocortisone acts primarily at the level of the galactosyltransferase.
Abbreviations: P-ado-P-S; 3′-phosphoadenosine-5′-phosphosulphate  相似文献   

17.
Viable human and murine lymphoblasts, and normal human tissue extracts, converted the thioether nucleosides 5'-methylthioadenosine (MeSAdo) and 5'-methylthioinosine (MeSIno) to methionine. Both MeSAdo and MeSIno, but not homocysteine, supported the short-term growth of human or murine lymphoblasts in methionine deficient medium. However, MeSAdo at concentrations greater than 25 microM inhibited cell growth. MeSIno was non-toxic at concentrations up to 200 microM, and supported the long-term growth of lymphoblasts in methionine-free medium.  相似文献   

18.
Six 2′-hydroxyflavonols were isolated from Gutierrezia microcephala, including four new compounds, 5,7,2′-trihydroxy-3,6,4′,5′-tetramethoxyflavone, 5,7,2′-trihydroxy-3,6,8,4′,5′-pentamethoxyflavone, 5,2′-dihydroxy-3,6,7,8,4′,5′-hexamethoxyflavone and 5,7,2′,4′-tetrahydroxy-3,8,5′-trimethxoyflavone and two known compounds, 5,7,2′,5′-tetrahydroxy-3,6,8,4′-tetramethoxyflavone and 5,7,2′,4′-tetrahydroxy-3,6,8,5′-tetramethoxyflavone.  相似文献   

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Two new flavanoids, characterized as 5,3′-dihydroxy-7,8,4′-trimethoxyflavanone and 5,3′-dihydroxy-6,7,4′-trimethoxyflavanone, have been isolated from the leaves of Vitex negundo.  相似文献   

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