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ATP allosterically activates the human 5-lipoxygenase molecular mechanism of arachidonic acid and 5(S)-hydroperoxy-6(E),8(Z),11(Z),14(Z)-eicosatetraenoic acid.

Smyrniotis CJ, Barbour SR, Xia Z, Hixon MS, Holman TR - Biochemistry (2014)

Bottom Line: 5-Lipoxygenase (5-LOX) reacts with arachidonic acid (AA) to first generate 5(S)-hydroperoxy-6(E),8(Z),11(Z),14(Z)-eicosatetraenoic acid [5(S)-HpETE] and then an epoxide from 5(S)-HpETE to form leukotriene A4, from a single polyunsaturated fatty acid.This work investigates the kinetic mechanism of these two processes and the role of ATP in their activation.Therefore, changes in ATP concentration in the cell could affect the production of 5-LOX products, such as leukotrienes and lipoxins, and thus have wide implications for the regulation of cellular inflammation.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry, University of California , Santa Cruz, California 95064, United States.

ABSTRACT
5-Lipoxygenase (5-LOX) reacts with arachidonic acid (AA) to first generate 5(S)-hydroperoxy-6(E),8(Z),11(Z),14(Z)-eicosatetraenoic acid [5(S)-HpETE] and then an epoxide from 5(S)-HpETE to form leukotriene A4, from a single polyunsaturated fatty acid. This work investigates the kinetic mechanism of these two processes and the role of ATP in their activation. Specifically, it was determined that epoxidation of 5(S)-HpETE (dehydration of the hydroperoxide) has a rate of substrate capture (Vmax/Km) significantly lower than that of AA hydroperoxidation (oxidation of AA to form the hydroperoxide); however, hyperbolic kinetic parameters for ATP activation indicate a similar activation for AA and 5(S)-HpETE. Solvent isotope effect results for both hydroperoxidation and epoxidation indicate that a specific step in its molecular mechanism is changed, possibly because of a lowering of the dependence of the rate-limiting step on hydrogen atom abstraction and an increase in the dependency on hydrogen bond rearrangement. Therefore, changes in ATP concentration in the cell could affect the production of 5-LOX products, such as leukotrienes and lipoxins, and thus have wide implications for the regulation of cellular inflammation.

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Detailed mechanism ofhydroperoxidation and epoxidation [dehydrationof 5(S)-HpETE to produce the epoxide]. Hydroperoxidationproceeds after initial abstraction of the pro-S hydrogenat C7, whereas epoxidation proceeds after abstraction of the pro-R hydrogen at C10.55 Theantarafacial nature of hydroperoxidation is well-known,31,47,79 while a suprafacial arrangementfor epoxidation was postulated by Jin et al.34
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fig2: Detailed mechanism ofhydroperoxidation and epoxidation [dehydrationof 5(S)-HpETE to produce the epoxide]. Hydroperoxidationproceeds after initial abstraction of the pro-S hydrogenat C7, whereas epoxidation proceeds after abstraction of the pro-R hydrogen at C10.55 Theantarafacial nature of hydroperoxidation is well-known,31,47,79 while a suprafacial arrangementfor epoxidation was postulated by Jin et al.34

Mentions: In comparing the proposed mechanisms of hydroperoxidation(oxidationof AA) and epoxidation (dehydration of the hydroperoxide to form theepoxide), we observed that they are similar but exhibit four key differences(Figure 2). First, the hydrogen atom is abstractedfrom C7 for hydroperoxidation but from C10 for epoxidation. Therefore,the positioning of the substrate will be distinct between the twoprocesses because the Fe(III)–OH moiety is proposed to be theactive species for both abstractions. Second, molecular oxygen doesnot attack the radical intermediate for epoxidation; rather, thereis a radical rearrangement producing the epoxide. Third, the Fe(II)–OH2 moiety donates a hydrogen atom to the peroxyl radical intermediateon C5 for hydroperoxidation but donates a hydrogen atom to a hydroxideradical for epoxidation, which is homolytically cleaved from the hydroperoxide.Finally, these two processes require different substrate rearrangementsteps to abstract a hydrogen atom from the substrate and donate itback to the intermediate. It is proposed that after abstraction ofa hydrogen atom from C7 and the antarafacial dioxygen attack, theFe(II)–OH2 moiety transfers an electron, via longrange, to the peroxyl radical intermediate.33 For epoxidation, the hydrogen atom is abstracted from C10; however,the Fe(II)–OH2 moiety is on the same side as thehydroperoxide, leading to a suprafacial homolytic cleavage of thehydroperoxide (Figure 2).34 This opens the possibility that the homolytic cleavageof the hydroperoxide by the Fe(II)–OH2 moiety toproduce the epoxide could possibly be achieved via an inner spherereduction, directly with the iron center.


ATP allosterically activates the human 5-lipoxygenase molecular mechanism of arachidonic acid and 5(S)-hydroperoxy-6(E),8(Z),11(Z),14(Z)-eicosatetraenoic acid.

Smyrniotis CJ, Barbour SR, Xia Z, Hixon MS, Holman TR - Biochemistry (2014)

Detailed mechanism ofhydroperoxidation and epoxidation [dehydrationof 5(S)-HpETE to produce the epoxide]. Hydroperoxidationproceeds after initial abstraction of the pro-S hydrogenat C7, whereas epoxidation proceeds after abstraction of the pro-R hydrogen at C10.55 Theantarafacial nature of hydroperoxidation is well-known,31,47,79 while a suprafacial arrangementfor epoxidation was postulated by Jin et al.34
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4215895&req=5

fig2: Detailed mechanism ofhydroperoxidation and epoxidation [dehydrationof 5(S)-HpETE to produce the epoxide]. Hydroperoxidationproceeds after initial abstraction of the pro-S hydrogenat C7, whereas epoxidation proceeds after abstraction of the pro-R hydrogen at C10.55 Theantarafacial nature of hydroperoxidation is well-known,31,47,79 while a suprafacial arrangementfor epoxidation was postulated by Jin et al.34
Mentions: In comparing the proposed mechanisms of hydroperoxidation(oxidationof AA) and epoxidation (dehydration of the hydroperoxide to form theepoxide), we observed that they are similar but exhibit four key differences(Figure 2). First, the hydrogen atom is abstractedfrom C7 for hydroperoxidation but from C10 for epoxidation. Therefore,the positioning of the substrate will be distinct between the twoprocesses because the Fe(III)–OH moiety is proposed to be theactive species for both abstractions. Second, molecular oxygen doesnot attack the radical intermediate for epoxidation; rather, thereis a radical rearrangement producing the epoxide. Third, the Fe(II)–OH2 moiety donates a hydrogen atom to the peroxyl radical intermediateon C5 for hydroperoxidation but donates a hydrogen atom to a hydroxideradical for epoxidation, which is homolytically cleaved from the hydroperoxide.Finally, these two processes require different substrate rearrangementsteps to abstract a hydrogen atom from the substrate and donate itback to the intermediate. It is proposed that after abstraction ofa hydrogen atom from C7 and the antarafacial dioxygen attack, theFe(II)–OH2 moiety transfers an electron, via longrange, to the peroxyl radical intermediate.33 For epoxidation, the hydrogen atom is abstracted from C10; however,the Fe(II)–OH2 moiety is on the same side as thehydroperoxide, leading to a suprafacial homolytic cleavage of thehydroperoxide (Figure 2).34 This opens the possibility that the homolytic cleavageof the hydroperoxide by the Fe(II)–OH2 moiety toproduce the epoxide could possibly be achieved via an inner spherereduction, directly with the iron center.

Bottom Line: 5-Lipoxygenase (5-LOX) reacts with arachidonic acid (AA) to first generate 5(S)-hydroperoxy-6(E),8(Z),11(Z),14(Z)-eicosatetraenoic acid [5(S)-HpETE] and then an epoxide from 5(S)-HpETE to form leukotriene A4, from a single polyunsaturated fatty acid.This work investigates the kinetic mechanism of these two processes and the role of ATP in their activation.Therefore, changes in ATP concentration in the cell could affect the production of 5-LOX products, such as leukotrienes and lipoxins, and thus have wide implications for the regulation of cellular inflammation.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Biochemistry, University of California , Santa Cruz, California 95064, United States.

ABSTRACT
5-Lipoxygenase (5-LOX) reacts with arachidonic acid (AA) to first generate 5(S)-hydroperoxy-6(E),8(Z),11(Z),14(Z)-eicosatetraenoic acid [5(S)-HpETE] and then an epoxide from 5(S)-HpETE to form leukotriene A4, from a single polyunsaturated fatty acid. This work investigates the kinetic mechanism of these two processes and the role of ATP in their activation. Specifically, it was determined that epoxidation of 5(S)-HpETE (dehydration of the hydroperoxide) has a rate of substrate capture (Vmax/Km) significantly lower than that of AA hydroperoxidation (oxidation of AA to form the hydroperoxide); however, hyperbolic kinetic parameters for ATP activation indicate a similar activation for AA and 5(S)-HpETE. Solvent isotope effect results for both hydroperoxidation and epoxidation indicate that a specific step in its molecular mechanism is changed, possibly because of a lowering of the dependence of the rate-limiting step on hydrogen atom abstraction and an increase in the dependency on hydrogen bond rearrangement. Therefore, changes in ATP concentration in the cell could affect the production of 5-LOX products, such as leukotrienes and lipoxins, and thus have wide implications for the regulation of cellular inflammation.

Show MeSH
Related in: MedlinePlus