Maleamate amidase that transforms maleamate into maleate and ammonia in the aerobic nicotinate degradation pathway. H2O + maleamate = maleate + NH4(+) Cofactor degradation; nicotinate degradation. Repressed by NicR in the absence of 6-hydroxynicotinate (6HNA) inducer. In presence of 6HNA, repression is alleviated. Belongs to the isochorismatase family.