Editing Urease (section)

====Blakeley/Zerner====

One mechanism for the catalysis of this reaction by urease was proposed by Blakely and Zerner.<ref name="pmid6788353">{{cite journal | vauthors = Dixon NE, Riddles PW, Gazzola C, Blakeley RL, Zerner B | title = Jack Jack Bean Urease (EC3.5.1.5). V. On the Mechanism of action of urease on urea, formamide, acetamide,N-methylurea, and related compounds | journal = Canadian Journal of Biochemistry | volume = 58 | issue = 12 | pages = 1335–1344 | year = 1979 | pmid = 6788353 | doi = 10.1139/o80-181 }}</ref> It begins with a nucleophilic attack by the [[carbonyl]] oxygen of the [[urea]] molecule onto the 5-coordinate Ni (Ni-1). A weakly coordinated water ligand is displaced in its place. A lone pair of electrons from one of the nitrogen atoms on the [[Urea]] molecule creates a double bond with the central carbon, and the resulting NH<sub>2</sub><sup>−</sup> of the coordinated substrate interacts with a nearby positively charged group. Blakeley and Zerner proposed this nearby group to be a [[Carboxylate|Carboxylate ion]], although deprotonated carboxylates are negatively charged.

A hydroxide ligand on the six coordinate Ni is deprotonated by a base. The carbonyl carbon is subsequently attacked by the electronegative oxygen. A pair of electrons from the nitrogen-carbon double bond returns to the nitrogen and neutralizes the charge on it, while the now 4-coordinate carbon assumes an intermediate tetrahedral orientation.

The breakdown of this intermediate is then helped by a sulfhydryl group of a [[cysteine]] located near the active site. A hydrogen bonds to one of the nitrogen atoms, breaking its bond with carbon, and releasing an {{NH3}} molecule.  Simultaneously, the bond between the oxygen and the 6-coordinate nickel is broken. This leaves a carbamate ion coordinated to the 5-coordinate Ni, which is then displaced by a water molecule, regenerating the enzyme.

The [[carbamate]] produced then spontaneously degrades to produce another ammonia and [[carbonic acid]].<ref name="Zimmer">{{cite journal | vauthors = Zimmer M | title = Molecular mechanics evaluation of the proposed mechanisms for the degradation of urea by urease | journal = J Biomol Struct Dyn | volume = 17 | issue = 5 | pages = 787–97 | date = Apr 2000 | pmid = 10798524 | doi = 10.1080/07391102.2000.10506568 | s2cid = 41497756 }}</ref>