Spectroscopic Evidence for a 4-Methylidene Imidazol-5-one in Histidine and Phenylalanine Ammonia-Lyases We thank Prof. G. E. Schulz and Dipl.-Chem. M. Baedeker (University of Freiburg) for providing us with the new PAL expression system and Dr. M. Stieger (Hoffmann-La Roche, Basel, Switzerland) for vector pREP4-GroESL carrying the HSP-60 system. D.R. and D.M. thank the Land of Baden-Württemberg for a scholarship for graduate students. The work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
Institut für Organische Chemie und Biochemie der Universität Richard-Willstätter-Allee, 76128 Karlsruhe (Germany).
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