Figure 12.

The urease enzyme catalyses the hydrolysis of urea to produce ammonia (NH₄) and carbonic acid (H₂CO₃). The substrate urea can be produced intracellularly as a by-product of respective metabolic reactions catalysed by the enzymes arginase and agmatinase. In the latter case, agmatine that is produced from l-arginine is converted via agmatinase to urea and the polyamine putrescine. Synthesis of putrescine can also occur via the arginase enzyme, which hydrolyses l-arginine to produce urea and l-ornithine. The amino acid l-ornithine can then be converted to putrescine or used for the production of other cellular compounds, such as proline. Both polyamines and proline have been implicated in other aspects of cellular metabolism, including melanin formation and the generation of ROS. It should be noted that putrescine synthesis is vital for the production of the polyamines spermidine and spermine via the enzymes spermidine synthase and spermine synthase, respectively. Solid arrows represent reactions observed during the present study, while the dotted arrows indicate hypothetical pathways obtained from literature. Compiled from our own results and from a review of literature (Wang and Casadevall 1994; Kingsbury et al. 2004; Morris 2004; Takagi 2008; Rutherford 2014; Kumar, Saragadam and Punekar 2015; Rocha and Wilson 2019).