An acidic zinc- and heme-containing protein was isolated from the soluble fraction of bovine brain and has been purified to homogeneity. The zinc-heme protein is a monomeric globular protein with a molecular mass of 31 200 Da as determined by electrospray mass spectrometry. The protein was isolated with 0.90 +/- 0.05 zinc per protein and with substoichiometric amounts of heme. Amino acid sequences of four peptides (ca. 20% of the protein) were determined and the comparison of these sequences with those of protein and gene sequence databases revealed no significant correlation with any known protein. Thus, it is concluded that it is a novel protein of currently unknown biological function.