Catalyzes the deamidation of nicotinamide, an early step in the NAD(+) salvage pathway. Positively regulates SIR2-mediated silencing and longevity by preventing the accumulation of intracellular nicotinamide, an inhibitor of SIR2, during times of stress. Acts also on nicotinyl hydroxamate. H2O + nicotinamide = NH4(+) + nicotinate Inhibited by N-ethylmaleimide, HgCl(2) and PCMB. Competitively inhibited by NAD, NMN and 3-acetylpyridine. Optimum pH is 6.5-7.5. Heating at 60 degrees Celsius inactivates the enzyme. Heating at 60 degrees Celsius in the presence of substrate prevents inactivation. Cofactor biosynthesis; nicotinate biosynthesis; nicotinate from nicotinamide: step 1/1. Concentrates in peroxisomes (PubMed:12736687). Induced during the stationary phase of growth, by calorie restriction, by various hyperosmotic shocks or by low-intensity stress (at protein level). Has a cis-peptide bond at 162-Val-Ala-163. Present with 7720 molecules/cell in log phase SD medium. Belongs to the isochorismatase family.