物理化学学 ̄(Wuli Huaxue Xuebao) January Aeta P .一C . .2012,28(1),213-216 doi:10.3866/PKU.WHXB201228213 2l3 www.whxb.pku.edu.cn [Article] 维生素K3的激发三重态与色氨酸、酪氨酸电子转移氧化反应的 激光闪光光解研究 唐睿智 李海霞 刘艳成 张鹏 曹西艳 。 王文锋 ( 中国科学院上海应用物理研究所,上海201800; 中国科学院研究生院,北京100049; 湖南科技大学化学化工学院,湖南湘潭411201) 摘要:利用时间分辨的激光闪光光解技术研究了乙腈一水混合溶液(1:1, 中2-甲基萘醌(通常称为维生素 K3)的激发三重态对色氨酸、酪氨酸的光敏氧化机理.通过瞬态吸收光谱的变化可以推断维生素Ka的激发三重 态可以与色氨酸、酪氨酸发生电子转移反应,反应形成的维生素K。阴离子自由基的吸收峰可以直接从瞬态吸收 谱图中观察到.维生素K。与色氨酸、酪氨酸的电子转移反应的速率分别为1.1X10。和0.6×10。L・mol~・S一.吉布 斯自由能(△G)的计算结果表明维生素K。的激发三重态与色氨酸、酪氨酸电子转移反应在热力学上是可行的. 关键词: 维生素K。:色氨酸: 酪氨酸;激光闪光光解 中图分类号:0644 Laser Flash Photolysis Study on Electron Transfer Oxidation Reaction of Tryptophan or Tyrosine with Triplet State Vitamin K3 1_ANG Rui.Zhi’- LI Ha1.Xia’, LIU Yan-Cheng ' WANG Wen—Feng’ lZHANG Peng’l CAO Xi.Yan’,。 Shanghai Institute fApploied Physics Chinese Academy ofSciences,Shanghai 20180 ̄P R.China; Graduate University fChioneseAcademy ofSciences,Beijing 100049, R.China; School ofChemist ̄and Chemical Engineering,Hunan Universiyt f oScience and Technology,Xiangtan 411201,Hunan Province,P R.China) Abstract:Laser flash photolysis was used to study the photosensitized oxidation mechanism of vitamin K3,commonly known as 2-methyl一1,4.naphthoquinone(MQ),with t ̄ptophan(TrpH)or tyrosine(myrOH)in acetonitrile/water(1:1, \/)solution.The triplet state of MQ reacted with TrpH or TyrOH by electron transfer with the formation of a MQ anion radicaI,which was directly obsewed in the transient absorption spectrum.The rate constants ofthe electron transfer reactions were determined to be 1.1 X10。and 0.6×10。 L・mol~・S~for TrpH and myrOH,respectively.The free energy changes(AG)of the reactions showed that the proposed electron transfer steps are thermodynamically feasible. Key Words:Vitamin K3:Tryptophan;myrosine;Laser flash photolysis 1 Introduction The photosensitized oxidation of biomolecule by photo—oxi— dation reaction has received increased aRention in recent years. The free radical theory of aging , shows that aging is a result tial targets for oxidation because they comprise approximately 68%of the dry mass of cells and tissues.Aromatic amino acid residues in proteins,especially tryptophan(TrpH)and tyrosine (TyrOH),are easily oxidized. Thus,the reactions of TrpH and TyrOH with photosensitizers have received considerable atten— of destructive effects on biomolecule.Proteins are major poten— Received:September 7,201l;Revised:October25,2011;Published onWeb:October 31,2011. ’Corresponding author.Email:wangwenfeng@sinap.ac.cn;Tel:+86・21・39194602. Theprojectwas supposedbytheNationalNatural ScienceFoundationofChina(21173252). 国家自然科学基金(21173252)资助项目 ⑥Editorial oicef ofActa Physico—Chimica Siniea 214 Acta Phys.一Chim.Sin.2012 、厂o1.28 tion in the field of proteins photo—oxidation. ~Oxidative dam— age to proteins occurs via complex chemical reactions that lead to changes in the proteins structure and the rupture of the poly— lamp was employed as detecting light source.The laser beam and analyzing light passed perpendicularly through a quartz cel1.The transmitted light entered a monochromator equipped with an R955 photomultiplier.The output signal from the HP545 1 0B digital oscillograph was transferred to a personal computer for study.The laser flash photolysis setup has been previously described. peptide chain as well as protein cross linking. The oxidative damage of proteins plays a critical role in the development of Alzheimer s disease,Parkinson s disease,cancer,and aging. 一 Vitamin K3,commonly known as 2-methyl一1,4一naphthoqui— none(MQ),is one of the widely used endogenous photosensi- tizers with antihemorrhagic activity.”MQ is present in vegeta— bles and plays an active role in the photosynthetic mechanism. It also participates in cellular respiration as an electron trans。 3 Results and discussion 3.1 Photoreaction of MQ with TrpH in acetonitrile/ water f1:1 l solution As shown in Fig.1.in the transient absorption spectrum after 355 nlTl laser flash photolysis of the N2-saturated acetonitrile/ porter,and in oxidative phosphorylation 一”as an effective elec— tron carrier and electron ffansfer agent. , Many studies have reported on the mechanisms of electron transfer oxidation of water(1:1)solution containing 0.1×10~mol・L~MQ,a maxi— mum absorption band at 370 am was observed.The triplet nucleotides by the triplet state of MQ( MQ )via laser flash photolysis technique. 。一 Charge transfer reactions between state absorption of MQ(at 370 nm)decays by a ifrst-order pro- cess with a rate of 3.4x 10 s一 in the N2.saturated acetonitrile/ ( MQ )and polyguanylic acid(polyG),guanine nucleotide (dGMP)demonsrtated that polyG radical cation,dGMP radical cation,and MQ radical anion can be detected simultaneously. In recent years.Basu et a1. 一 has been concerning and study. water(1:1)solution containing 0.1 x 10~mol・L~MQ.The maximum transient absorption at 370 nm can be quenched em— ciently by 02(Fig.1 inset).This result was similar to the report— ed triplet state absorption spectrum of MQ. ’ Fig.2 shows the transient absorption spectra after 355 am la- ing magnetic field effects(MFEs)and medium-dependent ef- fect on the photochemistry reactions between MQ and DNA, RNA bases,the results indicated that H atom transfer and elec— tron transfer are the operative mechanisms depending upon the ser flash photolysis of he N2t一saturated acetoniritle/water(1:1) solution containing 0.1×10~mol・L一。MQ and 0.2×10~mol・ L~TrpH.Under such conditions,the transient absorption of medium. However,to our knowledge,compared with the research on the rtiplet state of MQ appeared immediately at the end of the laser flash pulse,and decayed significantly faster in the pres- the triplet state of MQ reacting with nucleosides,fewer studies have discussed the oxidation of proteins by the triplet state of ence of TrpH.Following the decay of the triplet state of MQ at 370 nm,a spectrum with maximum absorption bands at 390 MQ,owing to its complicated structure and mechanism.There— fore,it is a signiicafnt task to elucidate the mechanisms of in- and 510 nnl appeared.The energy ofthe triplet(ET)ofMQ is about 239 kJ・mol~. while the 0f Trr)H is 297 kJ・mol-。. Therefore,the formation of the triplet state of TrpH via energy teraction between the triplet state of MQ and protein monomer units or complexes.In the current study,TrpH and Tlyr()H are selected as models to observe the photo--oxidation mecha・・ rtansfer from the triplet state of MQ is unlikely to occur.Ac— cording to previous reports,the maximum absorption of the nisms.We attempted to investigate the photo—processes of MQ with TrpH and TyrOH in acetonitrile/water(1:1,I1/ solutions using the 355 nm laser flash photolysis.The possible mecha- nisms are proposed and the related rate constants are obtained inthis study. MQ anion radical and I were l_ocated at 390 and 5 1 0 am,respectively.Consequently,the transient absorption spec- 0_25 2 Experi mentaI 2.1 Materials O.20 0.15 Vitamin K3(MQ),tryptophan(TrpH),tyrosine(TyrOH),and acetonitrile were purchased from Sigma-Aldrich.All the chemi— 0.10 cals were analytically pure and used as received without fur— ther puriicatfion.All solutions were prepared freshly with pure 0.05 water provided by Millipore puriicatfion system before each experiment.Samples were bubbled with high-puffty N2 or O5 0.00 300 (99.999%)for 20 min before laser flash photolysis.All solu- tions were buffered with phosphate(1×10~mol・L~,pH 7.0). 2.2 Methods 400 500 A,nm 600 700 Fig.1 Transient absorption spectra recorded at(▲)0.I/is and Nd:YAG laser(NL303H T’EKSPLA,Lithuania 1 provided 355 ntrl pulse with duration of 5 ns and the maximum energy of 8 mJ per pulse was used as the pump light source.A xenon (・)1 s after355 nm laserphotolysis ofO.1xlO mol・L MQ in N2-saturated acetonitrile/water(1:1)solution inset:transient time trace recorded at 370 nm in N2-saturated(a), 02-saturated(b)acetonitrile/water(1:1)solution 00c o_Jo∞o《 No.1 TANG Rui—Zhi et a1.:Laser Flash Photolysis Study on Electron Transfer Oxidation Reaction 2 1 5 O.30 O.25 ▲ ▲ ▲ ● ●▲ ● ▲ O.20 ● ● 0 15 8[∞qJo∞ 《 ▲● ▲ ▲ ▲● 0.10 ▲● ● ▲ ▲▲● O.O5 i・・・・- :::::::● ii ・毒・毒 0 00 300 400 500 600 A,nm Fig.2 Transient absorption spectra recorded at(▲)0.1 ps and (・)2 ps after 355 am laser photolysis of Nz-saturated acetonitrile/ water(1:1)solution containing lxl0一mol・L MQ and 2xl0一 nlol・L~TrplH inset:transient kinetic ̄aces recorded at(a】390 am and(b)510 am tra resulting from MQ reacting with TrpH can be explained by electron transfer rfom TrpH to the triplet state of MQ,generat— ing MQ anion radical and TrpH cation radical(TrpH”).Ac— cording to the p given in the literature, the TrpH”(pKa=4.3) turned into a neutral radical Trp。by deprotonation under the experimental conditions.As shown in Fig.2(inset),the forma— tion of MQ anion radical and Trp radical was synchronous with the decay of the triplet state of MQ.which further demon. strated the electron transfer reaction between the triplet state of MO andTrf}H. Varying the TrpH concentration f0.2 x 10~一0.7 x 10。mO1・ L ),the decay of MQ was accelerated in the presence of TrpH,with rates proportional to the concentrations of TrpH (Fig-31.the rate constant of the reaction was determined to be 1.1×10 L・mol~・s by monitoring the formation ofMO anion radical(Table 11.Thus.the mechanism of TrpH with the triplet state of M0 can be illus仃ated as the following: MQ +TrpH--- ̄MQ一‘/MQH。+TrpH /Trp 3.2 Photoreaction of MQ with TyrOH in acetonitrile/ water f1:1)solution Fig.4 shows the transient absorption spectra after 355 nm la. ser flash photolysis of the N2.saturated acetonitrile/water f1:11 solution containing 0.1 x 10。mo卜L~MQ and 0.2 x 10~mol・ T ∞ o Fig.3 Dependence of k。k at 390 am on the concentration of TrpH Table 1 Rate constants and free energy changes(aG)of electron transfer from TrpH and rOH t0 the triplet state of MQ L~Tyron.Similar to the photoreaction of MQ with TrpH,the transient absorption of the triplet state of MQ appeared imme— diately after laser flash pulse and decayed signiifcantly faster in the presence of TyrOH.However,after the decay of the trip. 1et state of MQ,a spectrum with only a maximum absorption at around 390 Bin formed.The transient absorbance of TyrOH”/ TyrO (at 410 nm)could not be observed clearly due to over- lapping with that of the MQ anion radical or its lower absorp— tion coemcient.The formation of the MQ anion radical was a1. so observed to be synchronous with the decay of the triplet state ofMQ rFig.4 inset).The formation oftriplet satte ofTyrOH via energy trnasfer from tirplet state of MQ is also unlikely to occur because the 1T of TyrOH(342 kJ。mol 1 is higher than that of MQ(239 kJ‘mol。。 .Therefore.It is concluded that the electron rtansfer rfom TyrOH to the rtiplet state ofMO also OC— curs.The rate constant of MO wiht TyrOH was acquired in a manner similar to the photoreaction of MO with TyrOH (Fig.5、.the rate constant of the reaction was detemrined to be 0.6 x 10 L・mol-1 ̄s~.The reaction mechanism of TyrOH with the triplet state of MQ can be illusrtated as following: MQ +TyrOH-*MQ /MQH。+T),roH“/Tyr0。 3.3 Calculation of the free energy changes(AG)for the electron transfer reactions To further prove the thermodynamic feasibility of the reac— tion,the free energy changes(AG)of the elecrton transfer be— tween the triplet state of MQ and TrpH or TyrOH can be calcu— lated by the Rehm—Weller equation: AG=96.48(Eo 一Eedme /ea)一Eoo where反 (in V1 and E (in V)are the oxidation potentials of the donor and the reduction potential of the accepto ̄respec. 0 4 O.3 ● 0.2 ▲ ▲ ▲● 0.1 ● ▲▲ ▲l▲●. ● 。: 0  ̄ ▲▲0000 ・・-t工il-。●・●台言 0.0 ●● 300 350 400 450 500 550 600 650 ,nm Fig.4 Transient absorption spectra recorded at(▲)0.1 ps and (・)3 Ils after 355 am laser photolysis of N2-saturated acetonitrile/ water(1:1)solution containing 0.1xl0~tool・L MQ and 0.2×10-3 mol・L TyrOH jnset:transient kinetic trace recorded at 390 nm 00c216 Acta Phys.一Chim.Sin.2012 、,oI.28 T ∞ ~∞ 。 0 10 [TyrOH],(tool・L ) Fig.5 Dependence of at 390 nm on the concentration ofTyrOH tively,and Eo,o(in kJ‘mol )is the triplet state energy of MQ. Here.e2/ed is the coulombic term.equa1 to 0.024 eV in acetoni- trile/water(1:1)solution. The and E0,o values of MQ are-0.77 V(vs saturated calomel electrode fSCE and 239.3 kJ。mol~,respectively.”The Eo values of TrpH and TyrOH are 1.O 1 and 0.93 V(vs normal hydrogen electrode(NHE)),re— spectively. Therefore,the AG values obtained for TrpH and TyrOH are-69.6 and-79.2 kJ‘mol~,respectively(Table 1). Thus,the photo—induced electron transfer from TrpH and Ty— r0H to the triplet state of MQ is thermodynamically favorable. 4 Conclusions The above experimenta1 results indicated that the triplet state of MQ reacted with TrpH and TyrOH by electron transfer with the formation of MO anion radical or oxidized radicals of Trp。and TyrO‘.The rate constants were determined to be 1.1x 10 and 0.6×10 L・mol~・s for TrpH and Tyr()H,respectively, and the free energy changes show that the electron transfer re- actions are thermodynamically feasible in ollr experiment. Knowledge of the electron transfer oxidation of TrpH and TyrOH by the rtiplet state of MQ is important to better under— stand structural effects on the photochemical behavior of pro- teins with the triplet state of MO. References (1)Finkel,T.;Holbrook,N.J.Nature 2000,408,239. (2)Harman,D. Geronto1.1957,2,298. (3)Davies,M.J.;Truscott,R.J.W Photochem.Photobio1.B Bio1.2001.63.114. (4)Silva,E.;ugarte,R.;Andrade,A.;Edwards,A.M. J.Photochem.Photobio1.B:Bio1.1994,63,43. (5)Jovanovic,S.V;Harriman,A.;Simic,M.G. 咖.Chem 1986,90,1935. (6)Lu,C.Y;Liu,Y Y.BBA—Gen.Subj.2002,1,71. (7)Zhang,P;Song,X.Y.;Li,H.X.;Yao,S.D.;Wang,、 F J.Photochem.Photobio1.A:Chem.2010,215,191. (8)Davies,K.J.A. fo em.1987,20,9895. (9)Viteri,G.;Edwards,A.M.;Fuente,J.D.L.Photochem Photobio1.2003,5,535. (10)Zhang,Z.X.;Hao,S.M.;Zhu,H.P.;Wang, F Photochem.Photobio1.B Bio1.2008,92,77. (11)Beal,M.F.Free.Radic.Bio1.Med.2002,32,797. (12)Levine,R.L,Free.Radic Bio1.Med.2002,32,790. (13)Hakh,O.;Karapire,C.;Posokhov,Y.;Icli,S. Photochem. Photobio1. Chem.2004,162,283. (14)He,Q.H.;Wang,Z.X.;Cao,X.X.;Chen,H.w;Ke,Y.F.Ana1. sct.2001,l 7,1209. (15)Vire,J.C.;Patriarche,G.J.;Christian,G.D.Ana1.Chem.1979, 51,752. (16)Chen,J.F.;Chu,G.S.;Zhang,Z.C.;Yao,S.D.;Lin,N.Y. Radiat.Phys.Chem 1999,55,35. (17)Perez—Ruiz, ;Maninez—Lozano,C.;Tomas,V;Martin,J. Talanta1999,50,49. (18)Berzas—Nevado,J.J.;Murillo・Pulgarin,J.A.;G6mez-Laguna, M.A. lanta 2001,53,951. (19)Dozal,A.;Keyzer,H.;Kim,H.K.;Wang,W Int. Antimicrob.Agents.2000,14,261. (20)Wagner,J.R.;VanLier,J.E.;Johnston,L.J.Photochem otobio1.1990,52,333. (21)Melvin, ;Bothe,E.;Schulte—Frohlinde,D.Photochem. Photobio1.1996,64,769. (22)Ma,J.H.;Lin, Z.;Du,F.Q.;Han,Z.H.;Yao,S D.;Lin,N. YSci ChinaBChem.2005,48,292. (23)Zhang,H.J.;Li,M.Y;Wang,P;Peng,J.;Wang,L.;Ai,X.C.; Zhang,X.K.;Zhang,J.E Chin Sci.Bul1.2004,49,2144. (24)Sengupta, ;Choudhury,S.D.;Basu,S. Am.Chem.Soc. 2004,126,1 0589. (25)Bose,A.;Basu,S. 脚 .Chem.A 2008,112,12045. (26)Bose,A.;Dey,D.;Basu,S. P .Chem.A 2008,112,4914. (27)Zuo,Z.H.;Yao,S.D.;Luo,J.;Wang,WF;Zhang,J.S.;Lin, N.Y Photochem.Photobio1. Bio1.1992,15,2 l 5. (28)Bose,A.;Dey,D.;Basu,S. Photochem.Photobio1. Chem. 2007,186,130. (29)Amada,I.;Yam@,M.Tsunoda,s.;Shizuka,H. Photochem. Photobio. Chem.1996,95,27. (30)Bensasson,R.V;Land,E.J.;Truscott,T.G.Flash Photolysis and Pulse Radiolysis—Contributions to the Chemistry ofBiology andMedicine;Oxford University Press:Oxford;1983;PP 93—110. (3 1)Solra,S.;Getoff,N.;Surdhar,P S.;Armstrong,D.A.;Singh,A. Phys Chem.1991,95,3639. (32)Tsentalovieh,Y P_;Snytnikova,O.A.;Sagdeev,R.Z. J Photochem Photobiol A Chem.2004 162,371 (33)Chu,G.S.;Zhang,S.J.;Yao,S.D.;Dou,D.Y;Zhang,Z.C. Acta .一Chim.Sin.2002,18,812.[储高升,张淑娟, 姚思德,窦大营,张志成.物理化学学报,2002,18,812.】 (34)Rehm,D.;Weller,D.1sr. Chem.1970,8,259. (35)Roger,J.E.;Kelly,L.A. Am.Chem.Soc.1999,121,3854. (36)Defelippis,M.R.;Murthy,C.P.;Faraggi,M.;Klappe ̄M.H. Biochemistry 1989,28,4847.