Precursor activation

Occasionally, an inactive precursor such as levodopa is converted to an active metabolite such as dopamine. 

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Fig. 9.12 An example of HPLC separation of the isoforms of Mycena citricolor luciferin precursors. The sample adsorbed on a PRP-lcolumn was eluted by a linear increase of acetonitrile from 20% to 40% in a pH 7.5 buffer containing 5 mM tributylamine sulfate. Practically all the peaks have the precursor activity.

Complement is not a single protein but comprises a group of functionally linked proteins that interact with each other to provide mar of the effector functions of humoral immunity and inflammation. Most of the components of the system are present in the serum as proenzymes, i.e. enzyme precursors. Activation of a complement molecule occurs as a result of proteolytic cleavage of the molecule, which in itself confers proteolytic activity on the molecule. Thus, many components of the system serve as the substrate of a prior component and, in turn, activate a subsequent component. This pattern of sequential activation results in the system being called the complement cascade. ... 

Sequence Protein precursor Activity Tumor Normal fibroblasts fibroblasts ... 

Most of the spectroscopic investigations discussed above were carried out on well-defined metallocene systems, either isolated species or those generated from a well-defined metallocene alkyl precursor activated with one equivalent of a borane or borate activator. Most practical polymerisation catalysts, on the other hand, include a scavenger, usually an aluminum alkyl, and may contain ill-defined activators such as methylaluminoxane (MAO), usually at high MAO/Zr ratios. Such systems are less amenable to quantitative studies nevertheless, the identifications of species such as those depicted in Schemes 8.5-8.8 has enabled similar compounds to be identified in more complex mixtures. An idea of the possible mode of action... 

Entry Precursor/ Activator Ligand Substrate S S/[Ni] t[h] Conv. l%] TOFfh 7 Select. ee[%]... 

A second pattern of allosteric control may be referred to as precursor activation or feed-forward control. 

PQQ See Pyrroloquinoline quinone Preproteins 519-522. See also Proenzyme(s) peroxisomal 521 Precursor activation 540 Prenatal diagnosis 26 Prenyl diphosphate (pyrophosphate) 390s Prenylation 402... 

The technologies that have been developed for the production of polyolefins, olefin homopolymers and copolymers are slurry, solution and gas-phase polymerisation bulk polymerisation of propylene in the liquid monomer as a special case of the slurry process has also emerged. The fundamental differences in the various olefin polymerisation processes reflect the different approaches that have been devised to remove the substantial heat of polymerisation. In addition, processes can be operated in a batch or a continuous mode. In the batch process the reagents are loaded into a polymerisation vessel, the polymer forms and the vessel is emptied before a new charge of reagents is introduced. In the continuous process, the catalyst precursor, activator and other necessary... 

In compartmentation systems (or precursor activation systems), precursors and activating enzymes work synergistically to exert plant defense however, other kinds of synergism were observed. For example, chemicals that enhance the toxicity of furanocoumarin by inhibiting detoxifying enzyme of insects (i.e., cytochrome P-450 monooxygenase) coexist with furanocoumarin in plants.5... 

Organometallic precursor Activation support Surface-bound metal species Characterization methods"... 

Development work of a complementary nature has been undertaken to improve the limits of detection of several fission and precursor activation products comprising Nb-94, Ag-108m and Ho-166m (long-lived 7-emitters) and Li as precursor to H-3. 

Third, as the proteinases complete their catalysis of precursor activation, they dissociate more completely from their respective complexes and are inactivated by the proteinase inhibitors present in the blood. Dissociation from the complexes is important in the complexes and in the presence of substrates, the proteinase inhibitors are blocked from reacting with the proteinases because the substrate obstructs access to the active site of the proteinase. 

The fibrinolytic system removes the fibrin of the hemostatic plug and thus is responsible for the temporary existence of the fibrin clot. The proteolytic action of plasmin on fibrin and fibrinogen is extensive and more like the digestive proteolysis catalyzed by trypsin and chy-motrypsin than the proteolysis involved in proteinase precursor activation. The fibrinolytic subsystem includes the reactions of plasminogen activation, plasmin inactivation, and fibrin digestion. As is common throughout the hemostatic system, irreversible activation reactions of the fibrinolytic system are opposed by irreversible proteinase inactivation. 

IL-5 CD4" T-lymphocytes (TH2 subset). bone marrow precursors Activation of B-lymphocytes and eosinophils, promotes IgE... 

Japanese researchers recognised the herbicidal precursor activity of 4-chloro-2-methyl(phenoxyethyl)-l-chloromethyl ether (21). 

Deoxyribonucleic Acid and Ribonucleic Acid Precursor Activity... 

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