ABSTRACT
H bond between its carbonyl oxygen and the side chain hydroxyl of Tyr 96. A different distal substrate binding site is present in other P450s.
The proximal ligand to the heme iron is cysteine (Fig. 18B). The cysteine ligand loop, consisting of eight residues around the proximal Cys, is conserved in all P450s. Like CPO, the Cys in P450 is at the positive N-terminal end of the proximal helix and the Cys sulfur is H-bonded to three peptide amides. On the distal side, in addition to substrate binding site, there are two highly conserved residues, Asp251 and Thr252, and a water chain connecting Thr252 and another highly conserved Glu366. Interestingly, two new water molecules are present in the distal pocket of the dioxy gen complex of P450cam (Fig. 18C) [218] and they may play important roles in the enzyme catalysis (see Sec. 4.2.5) [218,222].
