Malate synthase is one of the key enzymes of the glyoxylate cycle and is essential for growth on acetate as sole carbon source. The aceB gene from Corynebacterium glutamicum , encoding ma late sy n t hase, was is01 a ted, subcloned and expressed in Escherichia coli and C. glutamicum . Sequencing of a 3024 bp DNA fragment containing the aceB gene revealed that it is located close t o the isocitrate lyase gene aceA. The two genes are separated by 597 bp and are transcribed in divergent directions. The predicted aceB gene product consists of 739 amino acids with an M, of 82 362. Interestingly, this polypeptide shows only weak identity with malate synthase polypeptides from other organisms and possesses an extra N-terminal sequence of about 170 amino acid residues. Inactivation of the chromosomal aceB gene led to the absence of malate synthase activity and t o the inability to grow on acetate, suggesting that only one malate synthase is present in C. glutamicum. The malate synthase was purified from an aceB-overexpressing C. glutamicum strain and biochemically characterized. The native enzyme was shown to be a monomer migrating at an M, of about 80000. By sequencing the N-terminus of malate synthase the predicted translational start site of the enzyme was confirmed. The enzyme displayed K,,, values of 30 pM and 12 pM for the substrates glyoxylate and acetyl CoA, respectively. Oxalate, glycolate and ATP were found t o be inhibitors of malate synthase activity. The present study provides evidence that the malate synthase from C. glutamicum is functionally similar t o other malate synthase enzymes but is different both in size and primary structure.