Figure 1 - full size

Figure 1. Fig. 1. Stick diagrams overlaid with 2F[o]-F[c] density maps contoured at 1 (gray mesh), showing covalent attachment of substrate ligands to trypsin. Oxygens are colored red and nitrogens are colored blue for all structures; carbons are color-coded differently for the enzyme and ligand residues of each structure, as detailed below. (A) For AAPR-trypsin, enzyme carbons are green, and substrate carbons are yellow. (B) For AAPK-trypsin, enzyme carbons are light blue, and substrate carbons are tan. Both conformations of Ser-195 are shown. (C) For the leupeptin-trypsin hemiacetal, enzyme carbons are purple, and substrate carbons are orange. Both hemiacetal conformations are shown. (D) For guanidinobenzoyl-trypsin, enzyme carbons are teal, and substrate carbons are brown. The guanidinobenzoyl moiety is substantially rotated in the active site compared with the other substrate ligands. Consequently, positioning of the figure to clearly display substrate density removes the His-57 side chain from the viewing slab.