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71.
Insulin-activated protein kinases phosphorylate a pseudosubstrate synthetic peptide inhibitor of the p70 S6 kinase 总被引:8,自引:0,他引:8
p70 S6 kinase, a major insulin-mitogen-activated ribosomal S6 protein kinase in mammalian cells, is activated by phosphorylation of multiple Ser/Thr residues on the enzyme polypeptide. A synthetic peptide, corresponding to a 37-residue segment from the carboxyl-terminal tail of the kinase which resembles the sequence phosphorylated in S6, acts as a competitive inhibitor of p70 S6 kinase without itself being phosphorylated by the enzyme. This synthetic peptide is phosphorylated by an array of protein kinases which are rapidly activated by insulin. Thus, these sequences of p70 S6 kinase constitute a potential autoinhibitory pseudosubstrate site, whose phosphorylation is catalyzed by candidate upstream-activating protein kinases. 相似文献
72.
The epidermal growth factor (EGF) binding sites on bovine luteal cell membrane have been characterized in detail, and evidence has been obtained for a direct stimulatory effect of EGF on membrane-associated adenylate cyclase activity. The membrane fraction prepared showed the presence of high affinity (Ka = 1.2 +/- 0.7 x 10(-11) M-1), specific, and saturable EGF receptors of Mr = 170,000. The EGF receptors underwent rapid autophosphorylation and down-regulation following treatment of the cells with EGF. Treatment of the cells with 4 beta-phorbol 12-myristate 13-acetate resulted in a diminished binding of 125I-EGF to the receptors. When luteal cells were preincubated with EGF, both basal and forskolin-stimulated adenylate cyclase activity was increased severalfold. This enhancement of the adenylate cyclase activity was dependent upon the duration of the exposure to EGF and on the concentration of the growth factor. An optimal enhancement was observed when the cells were preincubated with 10 ng/ml EGF for 10-15 min. Furthermore, when the membrane fraction prepared from luteal cells was preincubated in vitro with EGF, a similar dose-related and time-dependent increase in basal, as well as forskolin-stimulated, adenylate cyclase activity was observed. These results demonstrate that luteal cell adenylate cyclase activity is finely regulated by EGF. Such a direct interaction between EGF and membrane-associated adenylate cyclase has not been previously recognized. 相似文献
73.
Manganese in cell metabolism of higher plants 总被引:1,自引:0,他引:1
Manganese, a group VII element of the periodic table, plays an important role in biological systems and exists in a variety of oxidation states. The normal level of Mn in air surrounding major industrial sites is 0.03 μg/m3, in drinking water 0.05 mg/liter and in soil between 560 and 850 ppm. Manganese is an essential trace element for higher plant systems. It is absorbed mainly as divalent Mn2+, which competes effectively with Mg2+ and strongly depresses its rate of uptake. The accumulation of Mn particularly takes place in peripheral cells of the leaf petiole, petiolule and palisade and spongy parenchyma cells. Mn is involved in photosynthesis and activation of different enzyme systems. Mn deficiency may be expressed as inhibition of cell elongation and yield decrease. Mn toxicity is one of the important growth limiting factors in acid soils. Plant tops are affected to a greater extent than root systems. The toxicity symptoms are, in general, similar to the deficiency symptoms. Toxic effects of Mn on plant growth have been attributed to several physiological and biochemical pathways, although the detailed mechanism is still not very clear. Higher O2 uptake and loss of control in Mn activated enzyme systems have been associated with Mn toxicity. Mn interferes with the uptake, transport and use of several essential elements including Ca, Fe, Cu, Al, Si, Mg, K, P and N. Excess of Mn reduces the uptake of certain elements and increases that of others. pH plays an important role in Mn uptake. Acidic pH causes a lack of substantial amount of nitrate as an alternative electron acceptor and leads to a high amount of Mn in leaves. High microbial activity, water logging and poorly structured soils cause severe Mn toxicity even in neutral soils. The molecular mechanism of Mn-tolerance is not yet clear. The level of tolerance is different in different species and seems to be controlled by more than one gene. Further information is required on the factors affecting the distribution, accumulation and membrane permeability of the metal in different plant parts and different species. Understanding of the genetic basis of Mn-tolerance is necessary to improve adaptation of crops against acid soils, water logging and other adverse soil conditions. 相似文献
74.
Acute mitochondrial insult has been suggested as a primary reason for the clinical, histopathological and biochemical abnormalities seen in Reye's syndrome. However, the etiology of mitochondrial dysfunction has not been identified. Polyamines have been known to alter the mitochondrial structure and function. Influenza infection may cause an increase in ornithine decarboxylase activity and thereby channel ornithine for polyamine biosynthesis, leading to mitochondrial dysfunction in Reye's syndrome. To test this hypothesis, the hepatic concentrations of polyamines, polyamine-metabolizing enzymes and urea cycle enzyme activities in Reye's syndrome patients were determined and compared with patients who died from illnesses other than Reye's syndrome. The hepatic concentration of putrescine, spermidine and spermine were increased in Reye's syndrome patients. The activity of ornithine decarboxylase was elevated but, due to the small number of samples, these values did not reach statistical significance. Ornithine carbamoyltransferase activity was decreased in the liver of Reye's syndrome patients. Our results suggest that increased synthesis of polyamines from ornithine may initiate mitochondrial injury in Reye's syndrome. 相似文献
75.
An array of insulin-activated, proline-directed serine/threonine protein kinases phosphorylate the p70 S6 kinase. 总被引:12,自引:0,他引:12
N K Mukhopadhyay D J Price J M Kyriakis S Pelech J Sanghera J Avruch 《The Journal of biological chemistry》1992,267(5):3325-3335
This study characterizes the insulin-activated serine/threonine protein kinases in H4 hepatoma cells active on a 37-residue synthetic peptide (called the SKAIPS peptide) corresponding to a putative autoinhibitory domain in the carboxyl-terminal tail of the p70 S6 kinase as well as on recombinant p70 S6 kinase. Three peaks of insulin-stimulated protein kinase active on both these substrates are identified as two (possibly three) isoforms of the 40-45-kDa erk/microtubule-associated protein (MAP)-2 kinase family and a 150-kDa form of cdc2. Although distinguishable in their substrate specificity, these protein kinases together with the p54 MAP-2 kinase share a major common specificity determinant reflected in the SKAIPS peptide: the requirement for a proline residue immediately carboxyl-terminal to the site of Ser/Thr phosphorylation. In addition, however, at least one peak of insulin-stimulated protein kinase active on recombinant p70, but not on the SKAIPS peptide, is present although not yet identified. MFP/cdc2 phosphorylates both rat liver p70 S6 kinase and recombinant p70 S6 kinase exclusively at a set of Ser/Thr residues within the putative autoinhibitory (SKAIPS peptide) domain. erk/MAP kinase does not phosphorylate rat liver p70 S6 kinase, but readily phosphorylates recombinant p70 S6 kinase at sites both within and in addition to those encompassed by the SKAIPS peptide sequences. Although the tryptic 32P-peptides bearing the cdc2 and erk/MAP kinase phosphorylation sites co-migrate with a subset of the sites phosphorylated in situ in insulin-stimulated cells, phosphorylation of the p70 S6 kinase by these proline-directed protein kinases in vitro does not reproducibly activate p70 S6 kinase activity. Thus, one or more erk/MAP kinases and cdc2 are likely to participate in the insulin-induced phosphorylation of the p70 S6 kinase. In addition to these kinases, however, phosphorylation of the p70 S6 kinase by other as yet unidentified protein kinases is necessary to recapitulate the multisite phosphorylation required for activation of the p70 S6 kinase. 相似文献
76.
Summary A method is described for non-radioactive labeling of total mRNA [poly(A)+ RNA] in plastic-embedded plant tissue sections. Oligo-deoxythymidylic acid (oligo-dT) labeled with digoxigenin-conjugated dUTP was used for in situ hybridization to poly(A)+ RNA in sections of tobacco (Nicotiana tabacum) anthers. The digoxigenin was immuno-stained using antidigoxigenin IgG and gold-labeled protein-A, followed by silver enhancement of the gold label. Reproducibly similar positive staining patterns were obtained with digoxigenin-labeled oligo-dT and polyuridylic acid [poly(U)], but not with a similarly labeled sense probe, poly(A). In the developing anthers, from the onset of meiosis to the production of pollen grains, labeling patterns were compatible with a gradual depletion of nuclear and chromosome-associated sporophytic mRNA molecules during prophase of meiosis, followed by postmeiotic production of gametophytic mRNA in microspore nuclei and the vegetative nuclei of the pollen grains.Abbreviations BSA
bovine serum albumin
- DIG
digoxigenin
- IgG
immunoglobulin-G
- oligo-dT
oligo-deoxythymidylic acid
- PAS-ABB
periodic acid Schiff-aniline blue black
- PBS
phosphate buffered saline
- poly(A)
polyadenylic acid
- poly(U)
polyuridylic acid
- SSC
standard saline citrate 相似文献
77.
A new technique for studying the effect of insulin on protein degradation is reported. The method is based on measuring the parallel release of a reutilizable and a nonreutilizable amino acid from muscle protein. Animals are prelabeled in vivo with [Me-3H]methionine which labels both the nonreutilizable 3-methylhistidine and the reutilizable methionine of tissue protein. The data presented show that insulin has only a trivial effect on the loss of 3-methylhistidine from muscle protein, while it substantially diminishes the efflux of methionine. The analysis of muscle protein confirms the observation that insulin causes the reincorporation of methionine and has a minimum effect on the loss of 3-methylhistidine. This supports the view that the major inhibitory effect of insulin on gluconeogenesis is the diversion of the flow of amino acids away from the gluconeogenesis pathway back toward protein synthesis. 相似文献
78.
A new antifungal antibiotic named acmycin was isolated from a soil streptomycete. Detailed comparative taxonomic studies showed
that the organism differed from three related species of streptomycetes. The organism was referred to asStreptomyces sp. AC2. The isolated antibiotic appears to be of polyene nature. 相似文献
79.
A soil actinomycete hydrolyzed collagen extracted from bovine Achilles tendon, calf skin, carp swim-bladder and rat tail tendon.
Glucose, mannose, aspartic acid and asparagine increased its collagenolytic activity which was optimum at 28 °C and at pH
7.2 – 7.5. Metallic ions, NaEDTA, cysteine, 4-chloromercuribenzoate, glutathione and sodium azide were inhibitory. 相似文献
80.
Girish Chandra 《BioControl》1980,25(2):187-192
Three new techniques of rearing dryinids parasitising rice hoppers were developed, namely, laboratory rearing technique for
detailed observations, device for transporting and rearing field-collected hoppers to estimate percentage parasitism and a
breeding technique.
Résumé Trois nouvelles techniques d’élevage de dryiinides parasites des cicadelles du riz ont été mises au point. L’une pour l’élevage en laboratoire en vue d’observations précises, un système pour le transport et l’élevage de cicadelles récoltées dans la nature afin d’évaluer le pourcentage de parasitisme et une technique d’élevage permanent.相似文献