Camphor binding

Figure 4. Energetics of (-)camphor binding to a-cyclodextrin in light (black lines) versus heavy water.

In the absence of substrate, the heme iron of P450cam is six-coordinate and low spin. Camphor binding expels all water molecules from the P450cam active site, and the iron becomes five-coordinate and high spin. 456 linear free-energy relationship has been observed between the P450cam spin state equilibrium and heme redox potential. The presence... 

The cloning of various P-450 enzymes has permitted the determination of their amino acid sequences (77). P-450cam of Pseudomonas putida (12) has recently been crystallized its structure was determined to 2.4 A resolution in 1984 (7i) and to 2.2 A resolution in 1986 (74). Figure 2 illustrates stereoscopic views of the camphor binding site, which clearly shows the hydrogen bonding interaction of the carbonyl oxygen of 7-camphor with the phenolic OH in Tyr-96(74). 

Volumetric analysis has been established and formalized by Chalikian (2003, 2011), and is capable of estimating the number of water molecules involved in reaction by measuring the changes in partial molar volumes of biomolecules. Partial molar volumes are obtained from the change of equilibrium when hydrostatic pressure is applied, in contrast to OSA s volume of water determined by the application of osmotic pressure (Shimizu 2004). Partial molar volumes can be measured from high-pressure experiments, as well as densitometry (Chalikian 2003, 2011). Here, the numbers of waters estimated from OSA and from volumetric analyses were often inconsistent. For instance, a fourfold difference was seen in the equilibrium dissociation of human IFN-y, and up to a threefold difference in the camphor binding of cytochrome P-450 (Shimizu 2004). 

Griffin BW, Peterson JA (1972) Camphor binding of Pseudomonas putida cytochrome P450. Kinetics and thermodynamics of the reaction. Biochemistry 11 4740 746... 

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