Synthesis urease-catalyzed

Fig. 14.13 Schematic illustration of the urease-catalyzed synthesis of CaC03 inside halloysite nanotubes.

Many enz5mies have been named by adding the suffix "-ase" to the name of their substrate or to a word or phrase describing their activity, e.g. UREASE catalyze hydrolysis of urea, MALTASE act on maltose, and DNA polymerase catalyze the synthesis of DNA. Other enzymes such as PEPSIN and TRYPSIN have names they do not denote their substrates. 

Fig. 8 Synthesis of amino acids by a multienzyme system consisting of leucine dehydrogenase (LeuDH) catalyzing the reductive amination of the corresponding keto acid, L-lactate dehydrogenase (l-LDH), and lactate for the regeneration of NADH and urease for the in situ generation of ammonia. The coenzyme NAD+ was covalently bond to dextran, enzymes and dextran-coupled NAD+ were...

Nickel is required for the synthesis of active urease in plant and other cells. The enzyme catalyzes the hydrolysis of urea to carbon dioxide and ammonia, via the intermediate formation of carbamate ion (equation 46). The molecular weight has been redetermined recently as 590 000 30 000, with six subunits. Each subunit has two nickel centres and binds one mole of substrate. The activity of the enzyme is directly proportional to the nickel content, suggesting an essential role for nickel in the enzyme. Several approaches, including EXAFS measurements, suggest that histidine residues provide some ligands to nickel, and that the geometry is distorted octahedral. There appears to be a role for a unique cysteine residue in each subunit out of the 15 groups present. Covalent modification of this residue blocks the activity of the enzyme. 

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