Catalyzes the reversible hydration of fumarate to (S)-malate (PubMed:22569531, PubMed:30645090). Catalyzes the hydration of fumarate to L-malate in the tricarboxylic acid (TCA) cycle to facilitate a transition step in the production of energy in the form of NADH (Probable). (S)-malate = fumarate + H2O Binds 1 [4Fe-4S] cluster per subunit. Specifically and competitively inhibited by 2-thiomalate, which coordinates with the catalytic [4Fe-4S] cluster. kcat is 28.3 sec(-1) for fumarate (in anaerobic conditions) (PubMed:22569531). kcat is 1.9 sec(-1) for fumarate (in aerobic conditions) (PubMed:22569531). kcat is 12.9 sec(-1) for (S)-malate (in anaerobic conditions) (PubMed:22569531). kcat is 0.55 sec(-1) for (S)-malate (in aerobic conditions) (PubMed:22569531). Optimum pH is 8.7. Carbohydrate metabolism; tricarboxylic acid cycle; (S)-malate from fumarate: step 1/1. Homodimer. Belongs to the class-I fumarase family.