Involved in the biosynthesis of polyamines which are thought to support the growth of thermophilic microorganisms under high-temperature conditions. It seems that long-chain and branched-chain of polyamines effectively stabilize DNA and RNA, respectively. Catalyzes the decarboxylation of N1-(3-aminopropyl)agmatine to yield spermidine and urea. It can also use agmatine to yield putrescine. H2O + N(1)-aminopropylagmatine = spermidine + urea agmatine + H2O = putrescine + urea Binds 2 manganese ions per subunit. kcat is 1.86 sec(-1) for ureohydrolase activity with agmatine as substrate (at pH 7.5 and 70 degrees Celsius). kcat is 1.01 sec(-1) for ureohydrolase activity with N(1)-aminopropylagmatine as substrate (at pH 7.5 and 70 degrees Celsius). Optimum temperature is 90 degrees Celsius. Amine and polyamine biosynthesis; spermidine biosynthesis. Cells lacking this gene show to a decreased growth rate at 85 degrees Celsius and a severe growth defect at 93 degrees Celsius. This mutant accumulates N1-aminopropylagmatine and agmatine at 85 degrees Celsius. In T.kodakarensis, two kinds of synthetic pathways from agmatine to spermidine are predicted. One is the pathway via putrescine (pathway I), and the other is that via N1-aminopropylagmatine (pathway II) (PubMed:20675472). Belongs to the arginase family.