Recombinant calprotectin, consisting of 2 individual peptide chains also called migration inhibitory factor-related protein (MRP)-8 and MRP14, was tested for antimicrobial activity in a Candida albicans growth inhibition assay. Both chains contain HEXXH zinc-binding sites and might be expected to manifest zinc-reversible, antimicrobial activity similar to that of native calprotectin. When tested alone, neither MRP8 nor MRP14 showed activity in the Candida growth assay. A synthetic 20-amino acid peptide containing the HEXXH sequence of MRP14, along with a nearby HHH sequence, was also inactive in this assay. However, equimolar concentrations of MRP8 and MRP14 demonstrated a potent growth inhibitory effect that was reversible by 30 microM zinc. Truncated MRP14 (missing the C-terminal GHHHKPGLGEGTP tail) used in combination with MRP8 demonstrated zinc-reversible activity that was somewhat less than that with complete MRP14. These results suggest that intact calprotectin, consisting of a heterodimer of MRP8 and MRP14, is necessary to form a zinc-binding site capable of inhibiting microbial growth.