Myristoyl-CoA:protein N-myristoyltransferase (NMT) is an essential eukaryotic enzyme that catalyzes the cotranslational transfer of myristate to the NH2-terminal glycine residue of a number of important proteins of diverse function. Human NMT (hNMT) activity was found to be activated by L-histidine in a concentration-dependent manner. In contrast, two structural analogues of L-histidine, L-histidinol and histamine, inhibited hNMT activity in a noncompetitive manner with half-maximal inhibitions of 18 and 1.5 mM, respectively. The inhibition of hNMT activity by L-histidinol was reversed by a 2-fold molar excess of L-histidine, suggesting that L-histidine and L-histidinol were competing for a common site on NMT. Kinetic data indicated that whereas L-histidine enhanced the Vmax, both L-histidinol and histamine decreased the Vmax; none of these compounds altered the Km. Our studies suggest that L-histidine and its analogues may be interacting with His-293, involved in myristoyl-CoA transfer, rather than His-218, and implicated in the transfer of myristoyl-CoA to the peptide substrates. Site-directed mutagenesis of His-293, Val-291, and Glu-290 resulted in proteins with no measurable NMT activity. The most conserved region in the catalytic domain EEVEH (289-293) is critical for the myristoyl-CoA transfer in the NMT-catalyzed reactions. This region will be useful for the design of regulators of NMT function.