Inhibition of histidine ammonia lyase by 8-methoxypsoralen and psoralen-oxidized photoproducts.
The effect of 8-methoxypsoralen-UVA therapy on the catalysis of histidine to trans-urocanic acid by histidine ammonia lyase (HAL, EC 4.3.1.3) was examined using an enzymatic assay from Sigma-Aldrich where the growth of the trans-urocanic acid peak at 277 nm was monitored. A Rayonet Photochemical Mini Reactor (Model RMR-600) equipped with eight, 3500 Å light sources and a custom UVA filter (Model S-BAL3 2.9 mm), from the Solar Light Company, were used to expose various reaction mixtures to broadband UVA light and UVA/UVB light. A UV-Vis spectrophotometer (Model Shimadzu UV 2540) with a temperature-controlled cell holder (Model TCC240) was used to monitor the growth of the trans-urocanic peak. Results of dark-binding experiments of 8-methoxypsoralen in denatured ethanol indicate no inhibition of enzyme activity due to ethanol but noncompetitive inhibition due to 8-methoxypsoralen. The effects of preirradiated 8-methoxypsoralen, with both broadband UVA and UVA/UVB, indicate that inhibition was due to psoralen-oxidized photoproducts. Inhibition of HAL was found when exposed to broadband UVA/UVB and to a lesser extent when exposed to broadband UVA.
Reilly
John T
JT
Department of Chemistry and Physics, Coastal Carolina University, Conway, SC, USA. jreilly@coastal.edu
Troester
Kyle A
KA
Tyner
Trista T
TT
Vitale
Dominick A
DA
Risher
Tiffiany R
TR
D006638:Histidine Ammonia-Lyase / Q000037:antagonists & inhibitors*; D006801:Humans; D007165:Immunosuppression Therapy; D008730:Methoxsalen / Q000494:pharmacology*; D010084:Oxidation-Reduction; D011701:PUVA Therapy; D055668:Photochemical Processes; D017319:Photosensitizing Agents / Q000494:pharmacology; D012871:Skin Diseases / Q000188:drug therapy / Q000201:enzymology / Q000276:immunology; D014560:Urocanic Acid / Q000378:metabolism
D017319:Photosensitizing Agents; D006638:Histidine Ammonia-Lyase; D014560:Urocanic Acid; D008730:Methoxsalen