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101.
Ronald J. Ash Gary A. Flynn Rob M.J. Liskamp Harry C.J. Ottenheijm 《Biochemical and biophysical research communications》1984,125(2):784-789
Sparsomycin, ScRs configuration, was the most potent of the four possible stereoisomers as a competitive inhibitor of peptide bond formation. In addition, the configuration of the two chiral centers dictated whether the compound exhibited time- and temperature-dependent inhibition of peptidyl transferase when incubated with polysomes prior to enzyme assay. The data corroborate the thesis that a peptidyl transferase-mediated acylation of the pivotal sulfoxide moiety and subsequent Pummerer rearrangement play a significant role in the inhibitory properties of sparsomycin. 相似文献
102.
Gary L. Stiles Ruth H. Strasser Brian F. Kilpatrick Sabrina R. Taylor Robert J. Lefkowitz 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,802(3)
Photoaffinity labeling techniques have recently demonstrated that mammalian β1- and β2-adrenergic receptors reside on peptides of Mr 62 000–64 000. These receptor peptides are susceptible to endogenous metalloproteinases which produce peptides of Mr 30 000–55 000. Several proteinase inhibitors markedly attenuate this process, specifically EDTA and EGTA. In this study we investigated the functional significance of this proteolysis (and its inhibition) in the β2-adrenergic receptor-adenylate cyclase system derived from rat lung membranes. Membrane preparations containing proteolytically derived fragments of the receptor of Mr 40000–55 000 are fully functional with respect to their ability to bind β-adrenergic antagonist radioligands such as [3H]dihydroalprenolol and β-adrenergic antagonist photoaffinity reagents such as p-azido-m-[125I]iodobenzylcarazolol. They retain the ability to form a high-affinity, agonist-promoted, guanine nucleotide-sensitive complex thought to represent a ternary complex of agonist, receptor and guanine nucleotide regulatory protein. Nonetheless, after proteolysis, GTP is less able to revert this high-affinity receptor complex to one of lower affinity, and all aspects of adenylate cyclase stimulation are reduced. In addition, the functional integrity of the N protein in membranes prepared without proteinase inhibitors is reduced as assessed by reconstitution studies with the cyc[su− variant of S49 lymphoma cell membranes. These results suggest that endogenous proteolysis does not directly impair the ability of β-adrenergic receptors to either bind ligands or interact with the guanine nucleotide regulatory protein. However, they imply that endogenous proteolysis likely impairs the functionality of other components of the adenylate cyclase system, such as the nucleotide regulatory protein. 相似文献
103.
Specific activities of eight enzymes involved in glycerol metabolism were determined in crude extracts of three strains ofNeurospora crassa after growth on six different carbon sources. One of the strains was wild type, which grew poorly on glycerol as sole carbon source; the other two were mutant strains which were efficient glycerol utilizers. A possible basis for this greater effeciency of glycerol utilization was catabolite repression of glyceraldehyde kinase by glycerol in wild type, and two-fold higher glycerate kinase activity in the mutant strains after growth on glycerol, thus apparently allowing two routes for glyceraldehyde to enter the glycolytic pathway in the mutant strains but only one in wild type. The preferential entry of glyceraldehyde to the glycolytic pathway through glycerate was suggested by the lack of glyceraldehyde kinase in all three strains after growth on one or more of the carbon sources and the generally higher levels of aldehyde dehydrogenase and of glycerate kinase than of glyceraldehyde kinase. 相似文献
104.
Richters Valda Elliott Gary Sherwin Russell P. 《In vitro cellular & developmental biology. Plant》1978,14(5):458-464
Summary The lungs of 12 mice, half of which were exposed to continuous 0.5 ppm nitrogen dioxide for 3 weeks, were explanted in culture,
and the instances of macrophage congregation were quantitated according to numbers of target cells involved, categories of
congregation from three to 11 or more, numbers of macrophages participating in each category for the total cultures, and the
influence of delaying explantation for 24 and 96 hr. A total of 9042 macrophages and 2140 epithelial and spindle target cells
were counted in the outgrowths from 306 explants. The incidence of macrophage congregation (or numbers of target cells) was
greater for the cultures from the NO2-exposed animals, both with respect to total incidences between groups (p→0), and the 0-hr (p<0.001) and 24-hr (p<0.01) culture
subgroups. In addition, the values for T3 to T6 macrophage congregation were individually and consistently greater for the exposed animal group. Postmortem interval stress
at 96 hr appeared to result in large colonies, but they were reduced greatly in number. Also the incidence of macrophage congregation
fell by 28% as compared to 0-hr and 24-hr subgroups.
Supported by Grants NHLI No. HL 17412 and EPA No. R. 800881. 相似文献
105.
Pravit Cadnapaphornchai Gary Aisenbrey Keith M. McDonald Thomas J. Burke Robert W. Schrier 《Prostaglandins & other lipid mediators》1978,16(6):965-971
Acute elevation of ureteral pressure to 100 mm Hg in anesthetized dogs (n=7) resulted in an increase (P<0.005) in systemic blood pressure from 151±7 to 163 ± 7 mm Hg, a transient (15 min) increase (P<0.05) in renal blood flow from 413 ± 27 to 465 ± 27 ml/min C and a rise (P<0.05) in plasma renin activity from 6.0 ± 1.6 to 10.3 ± 2.1 ng/ml/hr. Pretreatment with a competitive inhibitor of angiotensin II, i.e. sar1gly8AII, abolished the hypertensive response to acute ureteral obstruction, and pretreatment with 2 mg/kg of either indomethacin (n=6) or meclofenamate (n=3), 15 min before obstruction, prevented the hyperemic response. These results suggest that acute ureteral obstruction leads to hypertension via activation of the renin-angiotensin system and hyperemia via a prostaglandin-initiated mechanism. 相似文献
106.
Our previous studies have shown that 16 S RNA can assume two different conformational forms as detected by agarose gel electrophoresis, and that these two forms vary in their ability to bind individual 30 S ribosomal proteins specifically. In this paper we show that the faster electrophoretic form can be converted to the slower electrophoretic form by the binding of either protein S4, S8, S7 or S15. The slower form can then be transformed into a fast form by heat-activating the reconstitution intermediate (RI) particle, which has been constructed under reconstitution conditions at 0 °C, to RI1. We demonstrate that the transformation of the 16 S RNA conformation by binding of protein S7 permits the subsequent binding of protein S9 following deproteination. We propose that many of the classical assembly-dependent relationships are due to induced changes in the 16 S RNA conformation. 相似文献
107.
G. Lynis Dohm Gary R. Beecher Arthur L. Hecker Fernando R. Puente George J. Klain E. Wayne Askew 《Life sciences》1977,21(2):189-197
Experiments were conducted to investigate the influence of endurance exercise training on protein synthesis in skeletal muscle, heart, and liver. Training decreased incorporation of [14C]-leucine into proteins of the stromal fraction of muscle but there was no change in amino acid incorporation into proteins of the sarcoplasmic and myofibrillar fractions. Incorporation of [14C]-leucine into the protein of heart, liver, and plasma was depressed in trained rats compared to untrained rats. The specific radioactivity of [14C]-leucine was similar in tissues of trained and untrained rats and thus the depressed amino acid incorporation represents a decrease in the rate of protein synthesis. These observations demonstrate that the adaptation of muscle protein metabolism to endurance training is quite different than the alterations during work-induced hypertrophy of muscle. The difference in adaptation probably relates to the functional differences between the types of exercise. However depression of protein synthesis in trained rats is a general effect in several tissues and not an effect localized in muscle tissue. 相似文献
108.
John Leo Abernethy Gary F. Kuzmin Charles M. Lovett Jr. William A. Wilson 《Bioorganic chemistry》1980,9(4):440-449
Hydrazides of five N-acylamino acids have been used alone as substrates for papain catalysis to yield N1,N2-diacylhydrazines. With the exception of N-(benzyloxycarbonyl)(Z)-
-alanine hydrazide, they were very effective as both acylating agents of the enzyme and nucleophiles in attacking the enzyme-substrate intermediate. Although Z-
-alanine hydrazide was a minimal acylating agent, it was a satisfactory nucleophile. The most favorable reaction involved Z-
-alanine hydrazide in producing N1,N2-bis(Z-
-alanyl)hydrazine. When Z-
-alanine hydrazide was the substrate, this same chiral diacylhydrazine was formed along with meso N1-(Z-
-alanyl)-N2-(Z-
-alanyl)hydrazine. For the acylation step, the enzyme displayed powerful, essentially stereospecific, bias toward the
enantiomer. Once the thioester intermediate was formed, little preference was detected for attack by the enantiomers as nucleophiles. The most direct procedure for synthesis of substrates was conversion of Z-amino acids to their esters by means of dry HCl in an absolute alcohol. Treatment with hydrazine produced the hydrazides in excellent yield. 相似文献
109.
Metabolism of Dibenzo-p-Dioxin and Chlorinated Dibenzo-p- Dioxins by a Beijerinckia Species 总被引:7,自引:6,他引:1 下载免费PDF全文
Whole cells of the parent strain of Beijerinckia, grown with succinate and biphenyl, oxidized dibenzo-p-dioxin and several chlorinated dioxins. The rate of oxidation of the chlorinated dibenzo-p-dioxins decreased with an increasing degree of chlorine substitution. A mutant strain (B8/36) of Beijerinckia oxidized dibenzo-p-dioxin to cis-1,2-dihydroxy-1,2-dihydrodibenzo-p-dioxin. The mutant organism also oxidized two monochlorinated dibenzo-p-dioxins to cis-dihydrodiols. No metabolites were detected from two dichlorinated dibenzo-p-dioxins. Growth of the parent strain of Beijerinckia on succinate was inhibited after 4 h when 0.05% dibenzo-p-dioxin was present in the culture medium. Resting cell suspensions of the parent organism, previously grown with succinate and biphenyl, oxidized dibenzo-p-dioxin to a compound identified as 1,2-dihydroxydibenzo-p-dioxin. Further degradation of this metabolite was not detected, as the compound was found to be a potent mixed-type inhibitor of two ring-fission oxygenases present in this organism. 相似文献
110.
Fertilized eggs of Ilyanassa obsoleta form a protuberance which resembles a normal polar lobe when injected with Sr2+ or Ca2+ by microiontophoresis. Eggs also form a lobe-like protuberance when exposed to any of three drugs: compound , ionophore X537A, and ionophore A23187. Protuberances form more quickly and at lower drug concentrations if additional exogenous Ca2+ is added, whereas higher concentrations of Mg2+ do not have such an effect. When eggs are exposed to these drugs in Ca2+-, Mg2+-“free” seawater, with or without 10 mM EDTA, the eggs are still able to undergo extensive shape changes and form protuberances. Drug-induced shape changes are prevented by cytochalasin B, but will still occur in the presence of colchicine. Approximately 75% of Ilyanassa eggs are capable of forming and resorbing their third polar lobe and undergoing cytokinesis in Ca2+-, Mg2+-“free” artificial seawater (even containing 10 mM EDTA), solutions which by atomic absorption spectroscopy are shown to contain low concentrations of Ca2+ (3–5 μM) and Mg2+ (1.0–3.5 μM). The data suggest that if Ca2+ is required for normal polar lobe formation and cytokinesis, it is derived from intracellular sources or is required in only very low exogenous concentrations (i.e., less than 10?2 μM free Ca2+, in the presence of 10 mM EDTA). 相似文献