The Influence of Metal-complexing Agents on Citric Acid Production by Aspergillus niger

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Abstract
Amino acids liberated by peptidase hydrolysis of di-and oligopeptides by Pseudo-monas putida were measured by trinitrobenzenesulphonate assay and high voltage electrophoresis or paper chromatography followed by ninhydrin spray. Intact bacteria or periplasmic contents released by lysozyme treatment did not hydrolyse peptides. Subcellular fractionation showed that glycylmethionine peptidase activity was cytoplasmic. This enzyme had a Km of 2 mM, and was stimulated fivefold by I mM-Co2+. Crude peptidase extract did not cleave peptides with D-residues, acylated N-terminal amino groups or N-methylated peptide bonds but otherwise showed a wide specificity. Di-or tripeptides with blocked C-terminus were hydro-lysed. Leucylleucine (12 mM) and leucylglycylglycine (10 mM) did not compete with glycylmethionine (1–2 mM) and glycylmethionylglycine (I-o mM), respectively, for hydrolysis. Pseudomonas maltophilia also contained peptidase activity (0.84 μmol amino acid released from glycylmethionylglycine/min/mg protein). Peptidases of both P. putida and P. maltophilia were constitutive.