Investigation of Flavin-Containing DNA-Repair Model Compounds
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- 作者：Robert Epple ; Ernst-Udo Wallenborn ; and Thomas Carell
- 刊名：Journal of the American Chemical Society
- 出版年：1997
- 出版时间：August 13, 1997
- 年：1997
- 卷：119
- 期：32
- 页码：7440 - 7451
- 全文大小：597K
- 年卷期：v.119,no.32(August 13, 1997)
- ISSN：1520-5126
文摘
Irradiation of DNA with UV-B light causes the formation ofmutagenic DNA lesions such ascis-syn andtrans-syn cyclobutane pyrimidinedimers. DNA photolyases are flavin-dependent repair enzymes whichdirectlyrevert the mutagenic cis-synpyrimidine dimers into the corresponding monomers by alight-facilitated repair reaction.To gain deeper insight into the repair process, we recentlyprepared flavin-containing model compounds which areable to mimic the repair reaction (Carell, T.; Epple, R.; Gramlich, V.Angew. Chem., Int. Ed. Engl. 1996,35, 620-623). This publication now contains a detailed description of thesynthesis of a series of related model compoundsand a comprehensive investigation of their cleavage properties.The results obtained help to unravel the requirementsnecessary for an efficient, flavin-mediated cleavage of pyrimidinedimers and provide insight into the factors onwhich the enzymatic repair process depends. The investigation ofthe cleavage reaction with cis-syn,trans-syn,and trans-anti cyclobutanepyrimidine dimer model compounds reveal an enhanced vulnerability forthe cis-synisomer. The trans-syn dimer is10 times more stable. These results are comparable to thoseobserved in a recentstudy on the E. coli enzyme. The excellent solubilityof some of the model compounds has allowed a medium-dependent investigation of the flavin-initiated cleavage reaction.Increased cleavage efficiencies are observed inpolar solvents such as water (
= 0.06) and acetonitrile ( =0.05). The quantum yields decrease by a factor of 4in solvents with very low polarity such as dioxane ( = 0.01).These results are not in agreement with earliersolvent-dependent evaluations performed with non-flavin-containingmodel compounds (Hartzfeld, D. G.; Rose, S.D. J. Am. Chem. Soc. 1993, 115,850-854). The results, however, suggest that the unusually polarflavin-bindingpocket, observed in the X-ray crystal structure of the E.coli. photolyase, might be required to increase thecatalyticrepair efficiency. Investigations of the cleavage reaction in thepresence of acid and base in organic solvents emphasizethe strict requirement for a deprotonated reduced riboflavinchromophore. The determined pH values for half-maximal (pH = 6.5) and maximal (7 
pH 9) cleavage efficienciesare in agreement with the pKa value(pKa =6.3) of the reduced riboflavin and reveal that physiological conditionsare required to reach maximum catalyticcleavage efficiency.
= 0.06) and acetonitrile ( =0.05). The quantum yields decrease by a factor of 4in solvents with very low polarity such as dioxane ( = 0.01).These results are not in agreement with earliersolvent-dependent evaluations performed with non-flavin-containingmodel compounds (Hartzfeld, D. G.; Rose, S.D. J. Am. Chem. Soc. 1993, 115,850-854). The results, however, suggest that the unusually polarflavin-bindingpocket, observed in the X-ray crystal structure of the E.coli. photolyase, might be required to increase thecatalyticrepair efficiency. Investigations of the cleavage reaction in thepresence of acid and base in organic solvents emphasizethe strict requirement for a deprotonated reduced riboflavinchromophore. The determined pH values for half-maximal (pH = 6.5) and maximal (7 pH 9) cleavage efficienciesare in agreement with the pKa value(pKa =6.3) of the reduced riboflavin and reveal that physiological conditionsare required to reach maximum catalyticcleavage efficiency.