title: Effect of 5-deazaflavin on energy transduction during catalysis by Escherichia coli DNA photolyase.
abstract: DNA photolyase from Escherichia coli contains 1,5-dihydroFAD (FADH2) plus 5,10-methenyltetrahydropteroylpolyglutamate. The action spectrum observed for apoenzyme reconstituted with 5-deazaFADH2 (EdFADH2) matched its absorption spectrum after correction for the presence of a small amount of inactive 5-deazaFADox. The quantum yield for dimer repair with EdFADH2 (phi EdFADH2 = 0.110) was 6-fold lower than that observed with apoenzyme reconstituted with FADH2. Excited-state redox potential calculations indicate that 5-deazaFADH2 singlet is a better one-electron donor (E = -3.5 V) than FADH2 singlet (E = -2.7 V). Other studies indicate that the quantum yield for electron transfer from reduced flavin singlet to pyrimidine dimer (0.88) is unaffected when FADH2 is replaced by 5-deazaFADH2. Enhanced back electron transfer from pyrimidine dimer radical to flavin radical may account for the decreased quantum yield observed with EdFADH2 since, in the ground state, 5-deazaFADH. is a better oxidant than FADH.. The action spectrum observed for apoenzyme reconstituted with 5-deazaFADH2 plus 5,10-CH(+)-H4folate (EPtedFADH2) matched the absorption spectrum determined for enzyme-bound 5-deazaFADH2, indicating that the pterin chromophore was inactive as a sensitizer. This differs from results obtained with native enzyme, where pterin acts as a sensitizer via efficient singlet-singlet energy transfer to FADH2. The quantum yield for dimer repair by 5-deazaFADH2 bound to EPtedFADH2 (phi EPtedFADH2 = 0.0318) was 28.9% of that observed for EdFADH2. Spectroscopic studies indicate that singlet-singlet energy transfer in EPtedFADH2 is very efficient but only occurs in the "wrong" direction, i.e., from excited 5-deazaFADH2 to pterin.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biological Chemistry, Hahnemann University School of Medicine, Philadelphia, Pennsylvania 19102.
authors.forename: A J
authors.initials: AJ
authors.lastname: Ramsey
authors.forename: M S
authors.initials: MS
authors.lastname: Jorns
mesh_terms: D001051:Apoenzymes; D001665:Binding Sites; D004260:DNA Repair; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D004792:Enzyme Precursors; D004926:Escherichia coli / Q000201:enzymology*; D005415:Flavins / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D001051:Apoenzymes; D004792:Enzyme Precursors; D005415:Flavins; C019319:5-deazaflavin; D004255:Deoxyribodipyrimidine Photo-Lyase