Catalyzes the deamidation of nicotinamide (NAM) into nicotinate (PubMed:4399474, PubMed:8726014). Likely functions in the cyclical salvage pathway for production of NAD from nicotinamide (PubMed:4399474). Is also able to hydrolyze the first-line antituberculous drug pyrazinamide (PZA) into pyrazinoic acid in vitro, but this reaction is not considered to be physiologically relevant. H2O + nicotinamide = NH4(+) + nicotinate H2O + pyrazinamide = NH4(+) + pyrazine-2-carboxylate Optimum pH is 7.2. Cofactor biosynthesis; nicotinate biosynthesis; nicotinate from nicotinamide: step 1/1. Is constitutively expressed in very small amounts in E.coli. Belongs to the isochorismatase family.