PHOTOCHEMISTRY AND PHOTOBIOLOGY OF IMIDAZOLE-4(5)-METHYLIDENE MALONIC-ACID - AN ANALOG OF BOTH E-UROCANIC AND Z-UROCANIC ACID

Imidazole-4(5)-methylidene malonic acid (IMMA) may be thought of as ha ving its imidazole and carboxyl functionalities permanently fixed in a configuration that is simultaneously analogous to both E- (trans) and Z- (cia) urocanic acid (UA), Because the UA isomers affect the photoi nactivation of bacteriophage single-stranded DNA differently (E-UA inc reases and Z-UA decreases viral DNA inactivation), IMMA was similarly tested and was found to change the inactivation rate by a factor of 0. 43, which is intermediate between the values for E- and Z-UA (1.6 and 0.014, respectively), The IMMA likewise sensitizes double-stranded DNA by a factor of 10.3 compared to a value of 13 for UA, In several ways the effects of IMMA parallel the distinctive effects of UA on the UV inactivation of single- and double-stranded DNA, including the ability to prevent the formation of cyclobutane pyrimidine diners in irradiat ed single-stranded DNA and to sensitize a large increase in the format ion of those diners in irradiated double-stranded DNA. The IMMA photod ecarboxylates to UA with a low quantum efficiency (ca 1 x 10(-3)) and photochemically binds to calf-thymus DNA.