The characterization of a (nutritionally important) proline iminopeptidasefrom Eikenella corrodens

Eikenella corrodens generates energy primarily through the oxidative deamin ation of specific amino acids, a process that is coupled to dissimilatory n itrate reduction to nitrite. Cell yields resulting from chemostat-growth of the organism in simple, chemically defined media containing varying amount s of proline confirm that this amino acid is a likely source of energy for E. corrodens in the oral environment. The importance of proline in ATP gene ration by the organism is reflected in molar growth yields, which showed th at biomass production per mole of this amino acid was significantly higher than that for other amino acids. The organism was found to express, constit utively, the enzyme proline iminopeptidase, which releases proline from the N-terminus of small peptides. The enzyme was partially purified and charac terized and found to exist in the cytoplasm as a 35 kDa monomer. Inhibition studies showed that the enzyme, although classified as a serine protease, also appears to require thiol groups for activity, a finding which is consi stent with previous reports. The enzyme obeyed Michaelis-Menten kinetics an d was found to have a Km value of 0.223 mM for the substrate praline-p-nitr oanilide.