Glucose glycation reaction

Glycation reactions. Glucose or other sugars may react non-enzymatically with proteins to form glycation products. Early glycation products such as fructosamine-protein adducts may later be transformed to the more complex advanced glycation end products (AGE products). 

Fig. 5. Inactivation of Cu,Zn-SOD by glycation reaction in vitro. Purified Cu,Zn-SOD from human erythrocytes was incubated with 10-20 mAf glucose at 4°C under sterile conditions. At appropriate time intervals the SOD activity and thiobarbituric acid-reactive materials were measured.

Even though intraperitoneal injection of glucose suppressed Mn-SOD activity in the rat brain and heart (K2), unlike Cu,Zn-SOD, Mn-SOD did not undergo inactivation reaction due to glycation reactions. 

Glucose may auto-oxidize (like other alphahydroxy-aldehydes) and generate hydroxyl radicals in a transition-metal-catalysed reaction, and induce both fragmentation and conformational changes in glycated proteins (Hunt et al., 1990). 

Several markers for the Maillard reaction have been described in the literature. For example, the product initially formed between glucose and lysine is partly transformed into furosine (Heyns et ah, 1968) on acid hydrolysis. Conversely, the fluorescent amino acid pentosidine (Sell and Monnier, 1989) is an advanced glycation endproduct (AGE) and may form covalent bonds between proteins (cross-linking). Furthermore, the Maillard reaction leads to an increase in characteristic fluorescence (excitation 370 nm, emission 440 nm) (Monnier et ah, 1984 Pongor et ah, 1984). 

Bailey AJ, Sims TJ, Avery NC and Halligan EP (1995) Non-enzymatic glycation of fibrous collagen reaction products of glucose and ribose. Biochem J 305, 385-390. 

Figure 2.9. Glucose can enolize and reduce transition metals thereby generating superoxide free radicals (02" ), hydroxyl radicals ( OH), hydrogen peroxide (H202) and reactive dicarbonyl compounds. Adapted with permission from Wolff, S. P. (1996). Free radicals and glycation theory. In The Maillard Reaction. Consequences for the Chemical and Life Sciences, Ikan, R., ed., John Wiley Sons, Chichester, UK, 73-88.

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