guanosine and a water bind in the active site, does not matter in which order. The scissile N-1 glycosidic bond between the anomeric carbon and N9 of the base is broken resulting in an oxocarbenium transition state. The leaving group electrons are not protonated, but instead swing up to form a double bond between N9 and C8. The double bond that is already present on the purine swings out on N7 and is protonated by an active site histidine acting as a general acid. An active site aspartate acts as a general base, and deprotonates the water substrate molecule. The deprotonated water is then free to attack the transition state in a manner that will generate an αribose. Draw the active site and show how the mechanism works. You will need to draw 3 or 4 different active site “snap-shots” to show the entire process. Be sure to clearly show the transition state and how it might be stabilized
guanosine and a water bind in the active site, does not matter in which order. The scissile N-1 glycosidic bond between the anomeric carbon and N9 of the base is broken resulting in an oxocarbenium transition state. The leaving group electrons are not protonated, but instead swing up to form a double bond between N9 and C8. The double bond that is already present on the purine swings out on N7 and is protonated by an active site histidine acting as a general acid.
An active site aspartate acts as a general base, and deprotonates the water substrate molecule. The deprotonated water is then free to attack the transition state in a manner that will generate an αribose. Draw the active site and show how the mechanism works. You will need to draw 3 or 4 different active site “snap-shots” to show the entire process. Be sure to clearly show the transition state and how it might be stabilized
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