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Covalent Modifications of Enzymes and Cascade Effect

However, in most cases, covalent modifications can be either activation or deactivation and are normally energy-dependent and reversible, but catalyzed by separate enzymes. These include phosphorylation/dephosphorylation, adenylylation (nucleotidyla-tion)/deadenylylation and ADP-ribosylation (Stadtman and Chock, 1978). This cyclic interconversion of key enzymes between covalently modified and unmodified forms is a mechanism of singular importance in cellular regulation. The interconversion of an enzyme between the active and inactive forms involving separate modification and demodification (i.e. different converter enzymes) is a dynamic process that may lead to a steady state in a cascade system. The covalent interconversion of regulatory enzymes is characterized by  [Pg.375]

A theoretical analysis of cyclic cascades (Chock et al, 1980) reveals that  [Pg.375]

Adrenalin activates adenylate cyclase which synthesizes adenosine-3, 5 -cycUc monophosphate (cAMP), an activator of PrK. The enzyme (cAMP-dependent PrK) phosphorylates Ser and/or Thr (with consensus sequence of Arg-Arg-X-Ser/Thr-Y) of phosphorylase kinase consisting of C2R2. The binding of cAMP causes the dissociation of active catalytic monomers which utilizes ATP to phosphorylate phosphorylase b to the active phospho-phosphorylase a. The phosphorylation occurs at Serl4 of phosphorylase and requires Ca. The dephosphorylation of the active phospho form to the inactive dephospho form is catalyzed by PPrPl which becomes active when com-plexed with G-subunit The complexation of PPrPl(G) with its inhibitor releases phospho-(G) which is dephosphorylated to G-subunit by the action of PPrP2. [Pg.376]


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Covalent modification

Covalent modification of enzyme

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Effect of: covalency

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Enzymic modification

Modification of enzyme

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