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901.
荜拔中的新酰胺成分   总被引:1,自引:0,他引:1  
从荜拔地上部分乙醇提取物中分得5个化合物,经波谱分析确定其结构分别为:(α,β,α,β)-1,3-双(3,4-二甲基苯基)-2,4-双[1-(2-羰基-5,6-二氢吡啶)-甲酰基]-环丁烷(1)。  相似文献   
902.
The 8-methoxycarbonyloctyl glycosides of GlcNAc, Gal1-4Glc, Fuc1-2Fuc1-3GalNac and Fuc1-2Gal1-3[Fuc1-4]GlcNac were converted to primary amines by reaction with neat ethylenediamine and then coupled to bovine serum albumin (BSA) using diethyl squarate as the connector. The average degree of incorporation of the sugar onto the protein, as well as the molecular weight distribution, could be conveniently determined using matrix assisted laser desorption ionization/time of flight (MALDI-TOF) mass spectrometry thus avoiding cumbersome structure-dependent colour-tests or analysis of cleaved ligand. The present coupling method has the advantages of proceeding under very mild conditions, yielding controlled incorporation values and can reliably be used for the coupling of very small amounts (mg) of oligosaccharide.This paper is dedicated to Sen-itiroh Hakomori on the occasion of his 65th birthday  相似文献   
903.
Mannosyl-P-dolichol (man-P-dol) has been shown to stimulate the early reactions of the dolichol pathway, specifically, the biosynthesis of GlcNAc-P-P-dol and GlcNAc-GlcNAc-P-P-dol, and thus may play a regulatory role in glycoprotein biosynthesis. The site of action of man-P-dol has previously been suggested to be the GlcNAc-transferase concerned with the formation of the monoglucosaminyl derivative. Since the concentration of the chitobiosyl compound also increases as a result of the presence of man-P-dol, the immediate site of the activation was reexamined. The effect of man-P-dol on the formation of GlcNAc-GlcNAc-P-P-dol using GlcNAc-P-P-dol synthesizedin situ or added exogenously as the substrate was investigated. In addition, the distribution of radioactivity in the glucosaminyl constituents of the products under the stimulatory conditions was determined. The results of these studies supported the conclusion that the stimulation of GlcNAc-lipid synthesis by man-P-dol is due to the enhanced synthesis of GlcNAc-P-P-dol. It is not a result of the activation of the GlcNAc-transferase catalyzing the attachment of the second GlcNAc residue for the biosynthesis of the chitobiosyl derivative.Abbreviations GlcNAc-P-P-dol N-acetylglucosaminylpyrophosphoryldolichol - GlcNAc-GlcNAc-P-P-dol N-acetylglucosaminyl-N-acetylglucosaminylpyrophosphoryldolichol; - chito N-N-diacetylchitobiose - man-P-dol mannosylphosphoryldolichol - TX-100 triton X-100 - Tes 2-{[tris-(hydroxymethyl)-methyl]-amino}-ethanesulfonic acid  相似文献   
904.
    
Rat kidney-glutamylcysteine synthetase (GCS) was inactivated by reaction with trinitrobenzene sulfonate (TNBS), and the reaction followed pseudo-first-order kinetics. Inactivation kinetics revealed that only one of the amino acid residues modified by TNBS was essential for-GCS activity. The addition of 10 mM Mg2+ to the TNBS inactivation reaction resulted in a 16-fold increase in the rate of inactivation. Chromatographic analysis on the tryptic hydrolyzates of trinitrophenylated (TNP) derivatives showed that Lys-38 in theGCS heavy subunit was significantly modified in the presence of Mg2+. In contrast to small changes in the catalytic properties observed by mutation of Lys-38 to Arg, the mutants K38N and K38E had a marked decrease in enzymatic activity and about twofold increase inK m for glutamate. These results suggest that the positively charged Lys-38 may sbe involved in the binding of glutamate toGCS.  相似文献   
905.
Summary 1. Corticotropin-releasing factor (CRF) is thought to be involved in the regulation of the diurnal activity of the hypothalamus-pituitary-adrenal (HPA) axis and to act as a neurotransmitter in the brain. To date it is unknown whether the binding sites of the central CRF system are subject to diurnal variations. 2. We measured the number of CRF binding sites over the course of a complete 24-hr light-dark cycle in the pituitary, amygdala, bed nucleus of the stria terminalis (BNST), cingulate cortex, visceral cortex, paraventricular nucleus of the hypothalamus, hippocampus, and locus ceruleus of rats byin vitro receptor autoradiography with iodinated ovine CRF. A 24-hr time course was also established for plasma CRF and corticosterone. 3. The diurnal pattern of plasma CRF does not correlate with the pattern of plasma corticosterone. Within the brain, CRF binding in the basolateral nucleus of the amygdala showed a U-shaped curve with maximum levels in the morning and a wide hallow between 1500 and 0100. A biphasic profile with a small depression in the afternoon and a more pronounced depression in the second half of the activity period is characteristic for the other brain areas and the pituitary. The profile for the pituitary correlates with those for the BNST and the area of the locus ceruleus. Furthermore, the diurnal pattern of CRF binding sites in the BNST correlates with that of the hippocampus, and the daytime pattern of the visceral cortex is similar to that of both the hippocampus and the BNST. 4. Since the CRF-binding profiles in the brain and the pituitary clearly differ from the profiles of both plasma CRF and corticosterone, one may assume that the diurnal pattern of central CRF binding sites is not directly coupled to the activity of the HPA axis.  相似文献   
906.
Cathepsin B (EC 3.4.22.1) was purified from buffalo liver. The enzyme activity against-benzoyl-dl-arginine-naphthylamme (BANA) was substantially reduced by heat (above 37C) and by nondenaturing concentrations of urea (3 M) and guanidine hydrochloride (1 M). Cathepsin B was significantly activated by 1.5 mM EDTA alone. The activation of the enzyme was further enhanced in the presence of thiol compounds, e.g., cysteine thioglycolic acid, 2,3-dimercapto-1-propenol, and dithioerythritol (DTE). The minimum concentration of the thiol compound required for optimal activation of cathepsin B was found to be lowest (0.2 mM) for DTE. The BANA hydrolyzing activity of cathepsin B was substantially reduced by Cu2+ (20–200M) and Ca2+ (30–250 mM) as well as by thiol blocking reagents, e.g., iodoacetate, 5,5-dithiobis(2-nitro-benzoic acid) (DTNB), andp-hydroxymercuribenzoate (pHMB). The enzyme activity was completely abolished when the molar ratio of the reagent: cathepsin B was close to 1. The number of free sulfhydryl groups in cathepsin B was determined to be 2 by titration against DTNB and pHMB. Modification of one free thiol group of cathepsin B resulted in complete loss of BANA hydrolyzing activity.  相似文献   
907.
Computational sequence analysis of matrix metalloproteinases   总被引:12,自引:0,他引:12  
Matrix metalloproteinases (MMP) play a cardinal role in the breakdown of extracellular matrix involved in a variety of biological and pathological processes. Research on MMPs has classified and characterized these enzymes according to their matrix substrate specificity, gene and protein domain structure, and regulation of activity and expression. However, the discovery of new MMPs has introduced a need for a more comprehensive and systematic method of classification and quantitative comparison of known and newly discovered members. This study compiles a sequence alignment, constructs a dendrogram, and calculates physical data and homology percentage assignments in order to obtain further insight into MMP structure-function relationships. Thorough analysis of MMP primary sequence domains, physical data patterns, and statistical analysis of sequence homology yields higher resolution in the similarities and differences that group MMP members.  相似文献   
908.
Summary 1. In the rat, the LH-dependent ovarian progesterone rise mediates several actions of the primary surge of LH on the ovary. This experiment was aimed at elucidating the effects of the antiprogestagen RU486 on the LH-dependent decrease in both the serum concentrations and the ovarian content of inhibin.2. All rats in this experiment were treated with an antagonist of LHRH (1 mg/200 µl saline at 0800 h in proestrus) to supress the endogenous release of LH. One group of rats received 32 µg LH/250 µl saline at 1200 h in proestrus. Other group was given 4 mg RU486/200 µl oil at 0800 h in proestrus. The third group was injected with both RU486 and LH. Rats from the control group were injected with 250 µl saline and 200 µl oil. Animals were decapitated at 1700 h in proestrus and trunk blood and ovaries collected to determine the serum concentrations of LH, FSH, progesterone, 17ß-estradiol and inhibin as well as the ovarian content of inhibin.3. The ovulatory dose of LH in LHRHa-treated rats decreased both the serum concentrations and the ovarian content of inhibin and increased the serum concentrations of FSH. The administration of RU486 blocked the effect of LH on the serum concentrations of inhibin but not that on the ovarian content of inhibin.4. Since the antiprogestagen RU486 blocked the effect of LH on the serum concentrations of inhibin, we conclude that ovarian progesterone, besides mediating the effects of the primary LH surge on the ovulatory process and luteinization, participates in the LH-dependent drop in the serum concentrations of inhibin in proestrous afternoon.  相似文献   
909.
The circumstances that led to the discovery that plants luminesce after they are illuminated are described, as are other discoveries that would not have been possible were it not for the fortuitous association I had with my dear and most admirable friend, W.A. Arnold, to whom this special issue is dedicated.  相似文献   
910.
This paper evaluates and criticises the developmental systems conception of evolution and develops instead an extension of the gene's eye conception of evolution. We argue (i) Dawkin's attempt to segregate developmental and evolutionary issues about genes is unsatisfactory. On plausible views of development it is arbitrary to single out genes as the units of selection. (ii) The genotype does not carry information about the phenotype in any way that distinguishes the role of the genes in development from that other factors. (iii) There is no simple and general causal criterion which distinguishes the role of genes in development and evolution. (iv) There is, however, an important sense in which genes but not every other developmental factor represent the phenotype. (v) The idea that genes represent features of the phenotype forces us to recognise that genes are not the only, or almost the only, replicators. Many mechanisms of replication are involved in both development and evolution. (vi) A conception of evolutionary history which recognises both genetic and non-genetic replicators, lineages of replicators and interactors has advantages over both the radical rejection of the replicator/interactor distinction and the conservative restriction of replication to genetic replication.  相似文献   
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