Cynthia J. Krieger Peifen Zhang Lukas A. Mueller Alfred Wang Suzanne M. Paley Martha Arnaud John Pick Seung Yon Rhee Peter D. Karp MetaCyc: a multiorganism database of metabolic pathways and enzymes. 438-442 2004 32 Nucleic Acids Research Database-Issue db/journals/nar/nar32.html#KriegerZMWPAPRK04