engleski

In Search of Radical Intermediates in the Reactions Catalyzed by Lysine 2, 3-Aminomutase and Lysine 5, 6-Aminomutase

High-level ab initio calculations have been used to study radical intermediates in the reactions catalyzed by lysine 2, 3-aminomutase (2, 3-LAM) and lysine 5, 6-aminomutase (5, 6-LAM). The reactions of these enzymes with the substrate analogues 4-oxalysine (4-OL), 4-thialysine (4-TL), or trans-4, 5-dehydrolysine (t-4, 5-DL) are rationalized in terms of stabilization provided by the substituent to the adjacent radical center. Large changes in the exothermicity accompanying the initial H-abstraction are observed relative to the lysine reference values that follow the series 4-OL < 4-TL < t-4, 5-DL. These changes have the primary effect of increasing the endothermicity for subsequent ring-closure to form the putative aziridinylcarbinyl radical intermediate. Such stabilization is consistent with experimental observations of the substrate-derived radical (S) in the reaction of 2, 3-LAM with 4-TL as well as the ability of t-4, 5-DL to act as an irreversible inhibitor of 2, 3-LAM. Our calculations suggest that 4-TL and trans-3, 4-dehydrolysine may also permit experimental characterization of S radicals in the reactions catalyzed by 5, 6-LAM. Strategies for modifying PLP are presented that might lead to the first observation of the aziridinylcarbinyl radical intermediate (I) in the aminomutase-catalyzed reactions.

radical intermediates; aminomutase-catalyzed reactions

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