Catalysis formamide hydrolysis

Urease has a molecular weight of590 000 30 000 and consists of six identical subunits. Each subunit contains two Ni ions of different valency which are involved in substrate binding and conversion. The isoelectric point of the protein is at pH 5 and the temperature optimum of the catalysis at 60°C. The kinetic constants for urea hydrolysis have been determined to be k+2 = 5870 s"1 and Km = 2.9 mmol/1. Other amides, such as formamide and semicarbazide, react much more slowly than urea. The pH optimum of urease depends on the nature of the buffer used and, with the exception of acetate buffer, equals the pJTs value of the buffer. The active center of urease contains an SH-group that is essential for the stability of the enzyme. Complexing agents, such as EDTA and reductants, are required for stabilization. 

In addition to acid and base catalysis of amide hydrolysis, there is evidence that neutral water can also react with amides. A detailed investigation of the hydrolysis of formamide in aqueous solution was reported by Slebocka-Tilk et al. The value of the observed rate constant (Kbs) was found to depend on temperature because of the variation of the autodissociation equilibrium constant of water, Ky, with temperature. Log fcobs for the reaction at 56°C was a minimum at pH 6.1 and then increased in either more acidic or more basic environments. By measuring the rate constants for the acid- and base-catalyzed reactions, the investigators determined the rate constant for reaction of formamide with neutral water. Thus, the overall observed rate constant for the reaction at 56°C was... 

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