Enzyme Mechanism - Examples
In Lecture 10, I told you that many enzymes use the beta barrel shape to form their active site. Let's look at two examples of those type of enzymes. First, Triose-P Isomerase (TIM), which catalyzes the conversion of an aldehyde to a ketone. How does the 'perfect enzyme' work? Aldehydes are converted to ketones via an endiol intermediate. First, recall the structure of TIM from lecture 10.
Figure 20. Beta-barrel structure of TIM. The active site of TIM is at the top of the barrel where the lops joining the beta strands to the alpha-helix has the amino acid side chains which hold the triose-P substrate and catalyzes the interconversion between its aldose and ketose forms (ie the isomerization reaction).
Figure 21. The reaction catalyzed by TIM showing the ENE-diolate intermediate.
TIM has 3 AA's to catalyze the isomerization:
Glu-164, His-95, and Lys-13
The catalytic mechanism is illustrated below by conversion of ketone to aldehyde, which is OK since TIM catalyzes the interconversion equally well in either direction.
Figure 22. Catalytic mechanism of TIM.
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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu