eTopics

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eTopic 5.1 Some Alkaliphilic Enzymes Produce Useful Drug Delivery Systems

Cyclodextrin glucanotransferase is an industrially important enzyme produced by some alkaliphiles. This peculiar enzyme is capable of catalyzing the synthesis of non-reducing cyclic dextrins known as cyclodextrins, starting from starch, amylose, and other polysaccharides. The cyclodextrins are complex cyclic carbohydrates whose structure resembles a hollow, truncated cone with a hydrophobic (water-hating) core and hydrophilic (water-loving) exterior (Fig. 1). They are a superb vehicle for drug delivery. For example, cyclodextrins have been used in eyedrops to deliver the antibiotic chloramphenicol. The hydrophobic cavity of cyclodextrin can harbor a poorly soluble drug, while the hydrophilic exterior increases its apparent water solubility. The drug goes into solution more easily, permitting smoother absorption into the body.

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Figure 1  A cyclodextrin.  View down the channel in the hydrophobic core lined by C–O–C ether groups, which is surrounded by a hydrophilic exterior covered in −OH hydroxyl groups. The hydrophobic core can harbor drugs that are poorly soluble in water.