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121.
A bioconjugate of -chymotrypsin and Eudragit S-100 was used in an aqueous two-phase system (polyethylene glycol/phosphate) for casein hydrolysis. More product was obtained by replacing the lower salt phase with a fresh one during the reaction. The bioconjugate could be reused six times for casein hydrolysis. 相似文献
122.
A comparative study of two modifications of enzymic reduction of ethyl N-{2-{4-[(2-oxo-cyclohexyl)methyl]phe- noxy}ethyl} carbamate (1), an insect juvenile hormone bioanalog, was performed using Saccharomyces cerevisiae in two bioreactors of different size, 250-ml shake-flask and 1-l fermenter. The two major products of this reduction were obtained in 45–49% (w/w) yields but with > 99% enantiomeric purity. Their absolute configurations were assigned as ethyl (1S,2S)-N-{2-{4-[(2-hydroxycyclohexyl)methyl]phenoxy}ethyl}carbamate (2a) and ethyl (1R,2S)-N-{2-{4-[(2-hydroxycyclohexyl)methyl]phenoxy}ethyl}carbamate (3a). 相似文献
123.
Intracellular signal transduction pathways transmit signals from the cell surface to various intracellular destinations, such
as cytoskeleton and nucleus through a cascade of protein-protein interactions and activation events, leading to phenotypic
changes such as cell proliferation, differentiation, and death. Over the past two decades, numerous signaling proteins and
signal transduction pathways have been discovered and characterized. There are two major classes of signaling proteins: phosphoproteins
(e.g., mitogen-activated protein kinases) and guanosine triphosphatases (GTPases; e.g., Ras and G proteins). They both function
as molecular switches by addition and removal of one or more high-energy phosphate groups. This review discusses developments
that seek to quantify the signal transduction processes with kinetic analysis and mathematical modeling of the signaling phosphoproteins
and GTPases. These studies have provided insights into the sensitivity and specificity amplification of biological signals
in integrated systems. 相似文献
124.
Thymidyl-3,5-thymidine H-phosphonate undergoes acid, base, and water-catalyzed hydrolysis. The products were 3-thymidine H-phosphonate, 5-thymidine H-phosphonate, and thymidine in a ratio of 1:1:2. The rate constants are 1.8 × 10-3 M-1 sec-1, 7.2 × 103 M-1 sec-1, and 1.5 × 10-6 sec-1 for acid, base and water catalysis, respectively. These values are comparable with previous reports for the rates of hydrolysis of simple dialkyl esters of phosphorous acids. The Arrhenius activation energy for the base-catalyzed reaction is 20 kcal/mol. and the enthalpy and entropy of activation are 19 kcal/mol and –14 eu., respectively. The Gibbs free energy of activation is 23 kcal/mol. The rate constants suggest that nucleic acids linked by diesters of phosphorous acid hydrolyze too rapidly in aqueous solution to have accumulated in useful amounts on the primitive Earth. 相似文献
125.
The alternate pathway of signal transduction via hydrolysis of phosphatidylcholine, the major cellular phospholipid, has been investigated in murine peritoneal macrophages. A sustained formation of diacylglycerol, is preceded by an enhanced production of phosphatidic acid, when the macrophages were given a stimulus with 12-O-tetradecanoyl phorbol-13-acetate for sixty minutes. Production of choline and choline metabolites are significantly increased too. Propranolol, which inhibits phosphatidate phosphohydrolase, the enzyme responsible for conversion of phosphatidic acid to diacylglycerol, can effectively block the formation of diacylglycerol. Inhibition of protein kinase C either by its inhibitors, staurosporine and H-7 or by depletion, apparently affect the generation of the lipid products. Moreover, based on the results of transphosphatidylation reaction, involvement of a phospholipase D in the phosphatidylcholine-hydrolytic pathway in macrophages is predicted. These observations support the view that probably the phorbol ester acting directly on protein kinase C of the macrophages activate their phosphatidylcholine-specific phospholipase D to allow a steady generation of second messengers, to enable them to participate in the cell signalling process in a more efficient manner than those generated in the phosphoinositide pathway of signal transduction. (Mol Cell Biochem 000: 000-000,1999) 相似文献
126.
Human RhoA/RhoGDI complex expressed in yeast: GTP exchange is sufficient for translocation of RhoA to liposomes 下载免费PDF全文
Read PW Liu X Longenecker K Dipierro CG Walker LA Somlyo AV Somlyo AP Nakamoto RK 《Protein science : a publication of the Protein Society》2000,9(2):376-386
The human small GTPase, RhoA, expressed in Saccharomyces cerevisiae is post-translationally processed and, when co-expressed with its cytosolic inhibitory protein, RhoGDI, spontaneously forms a heterodimer in vivo. The RhoA/RhoGDI complex, purified to greater than 98% at high yield from the yeast cytosolic fraction, could be stoichiometrically ADP-ribosylated by Clostridium botulinum C3 exoenzyme, contained stoichiometric GDP, and could be nucleotide exchanged fully with [3H]GDP or partially with GTP in the presence of submicromolar Mg2+. The GTP-RhoA/RhoGDI complex hydrolyzed GTP with a rate constant of 4.5 X 10(-5) s(-1), considerably slower than free RhoA. Hydrolysis followed pseudo-first-order kinetics indicating that the RhoA hydrolyzing GTP was RhoGDI associated. The constitutively active G14V-RhoA mutant expressed as a complex with RhoGDI and purified without added nucleotide also bound stoichiometric guanine nucleotide: 95% contained GDP and 5% GTP. Microinjection of the GTP-bound G14V-RhoA/RhoGDI complex (but not the GDP form) into serum-starved Swiss 3T3 cells elicited formation of stress fibers and focal adhesions. In vitro, GTP-bound-RhoA spontaneously translocated from its complex with RhoGDI to liposomes, whereas GDP-RhoA did not. These results show that GTP-triggered translocation of RhoA from RhoGDI to a membrane, where it carries out its signaling function, is an intrinsic property of the RhoA/RhoGDI complex that does not require other protein factors or membrane receptors. 相似文献
127.
Tetanus Toxin Enhances Protein Kinase C Activity Translocation and Increases Polyphosphoinositide Hydrolysis in Rat Cerebral Cortex Preparations 总被引:2,自引:2,他引:0
Carles Gil Marisol Ruiz-Meana María Álava †Ephraim Yavin José Aguilera 《Journal of neurochemistry》1998,70(4):1636-1643
Abstract: Tetanus toxin (TeTx) has been recently demonstrated to be a Zn2+-dependent endopeptidase that cleaves synaptobrevin, a protein in part responsible for neurotransmitter release. Nevertheless, certain aspects of TeTx action, for example, the causal relationship between TeTx and protein kinase C (PKC; EC 2.7.1.37) activity cannot be explained by this cleavage alone. In the present study, primary neurons from fetal rat brain, synaptosomes, and whole slices have been used to examine this issue. Low doses of TeTx (≤ 10?8M) caused PKC activity translocation in a manner similar to that produced by 12-O-tetradecanoylphorbol 13-acetate (TPA). TPA (≤ 10?7M) caused sustained PKC activity translocation, whereas TeTx produced translocation followed by relocation, depending on the dose and time of exposure. Immunoidentification with a monoclonal antibody recognizing both α and β isoforms revealed that TeTx induced moderate losses of PKC in the cytosolic fraction, without a comparable increase in the particulate fraction. Although moderate losses of activity were also noticed in the cytosolic fraction, the inconsistency with respect to activity translocation may be explained by translocation of additional PKC isoforms that are not identified by the antibody. Comparable levels of water-soluble inositol phosphate-labeled intermediates were obtained after treatment of cerebral cells and/or cortical brain slices with TeTx. Significant increases of 19 and 114% in the water-soluble myo-[2-3H]inositol-labeled inositol phosphate metabolites were found in cerebral cell culture and brain slices, respectively, after treatment with 10?8M TeTx. TeTx (10?8M) increased to the same degree the water-soluble inositol phosphate levels as did serotonin (10?5M) or carbachol (10?6M). It is suggested that part of the signaling cascade of TeTx consists of a component involving inositol phospholipid hydrolysis, which is associated with PKC activity translocation. 相似文献
128.
Air-dried cells of Hansenula nonfermentans AKU 4332 catalyzed the production of (S)-3-pentyn-2-ol from (RS)-3- pentyn-2-ol acetate ester at 10% (v/v). The product was formed at 96.6% e.e. with a molar yield of 45% in 24 h. © Rapid Science Ltd. 1998 相似文献
129.
A biomimetic strategy in the synthesis and fragmentation of cyclic protein. 总被引:1,自引:0,他引:1 下载免费PDF全文
This paper describes a simple biomimetic strategy to prepare small cyclic proteins containing multiple disulfide bonds. Our strategy involves intramolecular acyl transfer reactions to assist both the synthesis and fragmentation of these highly constrained cyclic structures in aqueous solution. To illustrate our strategy, we synthesized the naturally occurring circulin B and cyclopsychotride (CPT), both consisting of 31 amino acid residues tightly packed in a cystine-knot motif with three disulfide bonds and an end-to-end cyclic form. The synthesis of these small cyclic proteins can be achieved by orthogonal ligation of free peptide thioester via the thia zip reaction, which involves a series of reversible thiol-thiolactone exchanges to arrive at an alpha-amino thiolactone, which then undergoes an irreversible, spontaneous ring contraction through an S,N-acyl migration to form the cyclic protein. A two-step disulfide formation strategy is employed for obtaining the desired disulfide-paired products. Partial acid hydrolysis through intramolecular acyl transfer of X-Ser, X-Thr, Asp-X, and Glu-X sequences is used to obtain the assignment of the circulins disulfide bond connectives. Both synthetic circulin B and CPT are identical to the natural products and, thus, the total synthesis confirms the disulfide connectivity of circulin B and CPT contain a cystine-knot motif of 1-4, 2-5, and 3-6. In general, our strategy, based on the convergence of chemical proteolysis and aminolysis of peptide bonds through acyl transfer, is biomimetic and provides a useful approach for the synthesis and characterization of large end-to-end cyclic peptides and small proteins. 相似文献
130.
Kwang Kim A. Louise Creagh Charles A. Haynes 《Biotechnology and Bioprocess Engineering》1998,3(2):71-77
The strain ofSerratia marcescens QM B1466 produces selectively large amount of chitinolytic enzymes (about 1mg/L medium). Enzymatic hydrolysis of chitin to
N-acetyl-β-D-glucosamine (NAG) was performed with a system consisting of two hydrolases (chitinase and chitobiase) produced
by optimization of a microbial host consuming chitin particles. For the development of Large-scale biological process for
the production of NAG from chitinaceous waste, the selection and optimization of a microbial host, particle size of chitin
and pretreatment of chitin source were investigated. Also, the effect of crab/shrimp chitin sources and initial induction
time using chitin as a sole carbon source on chitinase/chitobiase production and NAG production were examined. Crab-shell
chitin(1.5%) treated by dilute acid and, ball-milled with a nominal diameter less than 250m gave the highest chitinase activity
over a 7 days culture. Crude chitinase/chitobiase solution obtained in a 10 L fed-batch fermentation showed a maximum activities
of 23.6 U/mL and 5.1 U/mL, respectively with a feeding time of 3 hrs, near pH 8.5 at 30°C. 相似文献