We used ADH. Thanks for your help.
Fatima, you could discuss that the active site for ADH is suited for ethanol only, and so cannot catalytically convert the octanol due to its size.
Discuss properties of AHD's active site. An integral aspect of ADH's catalysis is the electrostatic stabilization of the alcohol's oxygen by a zinc atom; this make the proton on the alcohol more acidic. The catalytic zinc coordinates with two sulfurs from Cys 46, Cys 174 and His 67. An ionizable water molecule occupies the 4th position on the zinc. The water molecule is also hydrogen bonded tothe hydroxyl group of Thr-48. The 5th and final zinc coordinate is, of course, the oxygen from the alcohol.
ADH catalyzes the oxidation of alcohols by reducing NAD with a hydride. ADH also utilizes a zinc ion to electrostatically stabilize the alcohol oxygen, thus increasing the acidity of the alcohol's proton. In the pathway, His 51 is activated by general base catalysis such that the histidine can then accept a proton from the NAD, which in turn draws a proton from Thr 48, again demonstrating general base catalysis (although this is rather indirect since the substrate has not yet been involved). These proton transfers ready the threonine (which is negatively charged due to proton transfer to the NAD) for accepting a proton from the alcohol of the actual substrate (cyclohexanol in the case of this particular model). This is the first example of true base catalysis actually involving the substrate. At the same time, since this oxidation is concerted, there is a hydride transfer to the NAD in its traditional hydride accepting region. Thus, the whole sequence essentially amounts to a transfer of hydride to the NAD and the oxidation of an alcohol to an aldehyde. Key points are the orientation of the amino acid proton acceptors and donors, as well as the position of the zinc ion in relation to the substrate such that it stabilizes a negative charge on the substrate thereby taking part in transition state stabilization.
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