Mechanism of Activation
In a tissue where active β-galactosidase is present, the sugar will be cleaved from the rest of the compound. This permits water to access the paramagnetic center, and causes the magnetic relaxation properties of the surrounding water molecules to change. This change in relaxation times will, in turn, visibly alter the signal intensity of images of the tissue obtained from MR scans.
The mechanism proceeds in the same manner as all other β-galactosidase-catalyzed cleavages. The carboxyl group on a glutamic acid side chain within the enzyme acts as an acid catalyst, hastening the cleavage of the glycosidic bond at the C-1 position in the sugar. This cleavage gives water access to the paramagnetic center. The result of the enzyme-catalyzed reaction is a free galactose molecule and an activated contrast agent.
Read more about this topic: Enzyme-activated MR Contrast Agents
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