Stereospecificity of folate binding to DNA photolyase from Escherichia coli.

DNA photolyase from Escherichia coli contains folate ([6S]-5,10-CH(+)-H4Pte(Glu)n = 3-6) and reduced FAD. The folate chromophore acts as an antenna, harvesting light energy which is transferred to the reduced flavin where DNA repair occurs. The folate binding stereospecificity of the enzyme was investigated by reconstituting the apoenzyme with [6R,S]-5,10-CH(+)-H4folate and reduced FAD. The isomer composition of [methyl-3H]-5-CH3-H4folate, released into solution upon reduction of the reconstituted enzyme with [3H]NaBH4, was analyzed by enzymatic and chiral chromatographic methods. Both methods showed that the reconstituted enzyme contained nearly equimolar amounts of [6R]- and [6S]-5,10-CH(+)-H4folate.