Enzyme-bound generation

This phosphotransferase [EC 2.7.2.1] catalyzes the thermodynamically favored phosphorylation of ADP to form ATP Aeq = [ATP][acetate]/ [acetyl phosphate] [ADP] = 3000). GDP is also an effective phosphoryl group acceptor. This enzyme is easily cold-denatured, and one must use glycerol to maintain full catalytic activity. Initial kinetic evidence, as well as borohydride reduction experiments, suggested the formation of an enzyme-bound acyl-phosphate intermediate, but later kinetic and stereochemicaT data indicate that the kinetic mechanism is sequential and that there is direct in-line phosphoryl transfer. Incidental generation of a metaphosphate anion during catalysis may explain the formation of an enzyme-bound acyl-phosphate. Acetate kinase is ideally suited for the regeneration of ATP or GTP from ADP or GDP, respectively. 

One unit of immobilised enzyme is defined as the amount of enzyme bound to glass beads that generates 1 pmol NADH/min under standard assay conditions . BA concentration in the serum and bile is extrapolated from the standard curve be-... 

Fe2+ to generate an enzyme-bound iron-oxygen complex, and ascorbic acid (vitamin C) to subsequently reduce this complex. 

NOS catalyzes two sequential monooxygenase reactions. First, NOS hy-droxylates L-arginine (132) to generate an enzyme-bound intermediate, N-hydroxy-L-argininc (133). Then, 133 is further oxidized to generate nitric oxide ( NO) and citrulline (134) [128] (Scheme 29). 

The metalloproteases (MPs) and matrix metalloproteinases (MMPs) are a class of metallohydrolases of particular interest to the pharmaceutical industry due to their role in a number of pathological processes [81-83], The lack of an enzyme-bound nucleophilic residue in the metallohydrolases complicates the design of ABPP probes for this class of enzymes. Rather than mechanism-based and electrophilic probes for ABPP, photoreactive variants of reversible inhibitors of metallohydrolases have been developed [84-86]. These reversible inhibitors usually contain a hydroxamate moiety that is capable of chelating the catalytic zinc ion in a bidentate manner [79, 80]. The hydroxamate moiety was incorporated into the first generation of metallohydrolase ABPP probes along with a benzophenone group capable of covalent bond formation upon UV irradiation (Scheme 4). 

P-Elimination and then replacement reaction of an a-amino acid with a nucleophile is very attractive from the viewpoint of synthetic organic chemistry because various P-substituted alanines may be prepared from a simple a-amino acid, such as serine, and nucleophiles. A reaction catalyzed by tryptophan synthase - the formation of tryptophan from serine and indole - is one of the most well-known P-elimination and replacement reactions (Scheme 2.7). Here, an aldimine Schiff base is derived from reaction of the enzyme-bound PLP with serine, which then dehydrates to give the Schiff base of PLP with 2-aminoacrylate. Indole then adds to the vinyl Schiff base, generating tryptophan after lysine aminolysis of the Schiff base product. 

M(VI) and M(IV) oxidation states. The M(V) state is generated by a one-electron reduction of the M(VI) state, or the one-electron oxidation of the M(IV) state, and occurs during the catalytic cycle—en route to the regeneration of the catalytically active state. Spectroscopic studies of the Mo—MPT enzymes, notably electron spin resonance (EPR) investigations of the Mo(V) state, have clearly demonstrated that the substrate interacts directly with the metal center (37). The first structural characterization of a substrate-bound complex was achieved for the DMSOR from Rhodobacter capsulatus DMS was added to the as-isolated enzyme to generate a complex with DMSO that was O-bound to the molybdenum (43). 

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