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Aspartyl aminopeptidase (EC 3.4.11.21) cleaves only unblocked N-terminal acidic amino-acid residues. To date, it has been found only in mammals. We report here that aspartyl aminopeptidase activity is present in yeast. Yeast aminopeptidase is encoded by an uncharacterized gene in chromo-some VIII ( 1 YHR113W, Saccharomyces Genome Database). | iFEBS Journal Identification of yeast aspartyl aminopeptidase gene by purifying and characterizing its product from yeast cells Ryo Yokoyama Hiroshi Kawasaki and Hisashi Hirano Supramolecular Biology InternationalGraduate Schoolof Arts and Sciences Yokohama City University Japan Keywords aspartyl aminopeptidase evolution M18 family of metalloproteases matrix-assisted laser desorption ionization time-of-flight mass spectrometry Correspondence Dr. Hiroshi Kawasaki Yokohama City University Maioko-cho 641-12 Totsuka-ku Yokohama Kanagawa 244-0813 Japan E-mail kawasaki@yokohama-cu.ac.jp Present address Laboratory for Immunogenomics Research Center for Allergy and Immunology Institute of Physicaland ChemicalResearch 1-7-22 Suehiro Tsurumi Yokohama 230-0045 Japan Aspartyl aminopeptidase EC 3.4.11.21 cleaves only unblocked N-terminal acidic amino-acid residues. To date it has been found only in mammals. We report here that aspartyl aminopeptidase activity is present in yeast. Yeast aminopeptidase is encoded by an uncharacterized gene in chromosome VIII YHR113W Saccharomyces Genome Database . Yeast aspartyl aminopeptidase preferentially cleaved the unblocked N-terminal acidic amino-acid residue of peptides the optimum pH for this activity was within the neutral range. The metalloproteases inhibitors EDTA and 1.10-phenanthroline both inhibited the activity of the enzyme whereas bestatin an inhibitor of most aminopeptidases did not affect enzyme activity. Gel filtration chromatography revealed that the molecular mass of the native form of yeast aspartyl aminopeptidase is w 680 000. SDS PAGE of purified yeast aspartyl aminopeptidase produced a single 56-kDa band indicating that this enzyme comprises 12 identical subunits. Received 8 September 2005 revised 6 November 2005 accepted 9 November 2005 doi 10.1111 j.1742-4658.2005.05057.x Although sequencing of the yeast genome was completed several years ago protein databases still contain numerous hypothetical proteins that have yet
