1EPO:
reference: Direct observation by X-ray analysis of the tetrahedral "intermediate" of aspartic proteinases., Veerapandian B, Cooper JB, Sali A, Blundell TL, Rosati RL, Dominy BW, Damon DB, Hoover DJ, Protein Sci 1992 Mar;1(3):322-8. PMID: 1304340

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