Synergistic action of ultraviolet radiation and hydrogen peroxide on citrulline.

Citrulline/Ultraviolet radiation/Hydrogen peroxide /Photo degradation Ultraviolet irradiation of citrulline in the presence of hydrogen peroxide formed aspartic acid, glutamic acid, glycine, ƒ¿-aminobutyric acid, norvaline, arginine and two unidentified ninhydrin-reactive products. Irradiation of citrulline, both in the presence and absence of hydrogen peroxide, formed ammonia and urea. The reactions followed the first-order kinetics with increased reaction constants in the presence of hydrogen peroxide. Without UV light, hydrogen peroxide itself had no effect on citrulline. Ionizing radiation produces hydrogen peroxide in oxygenated aqueous me dium and forms hydroxyl radicals by radiolysis of watery. Peroxide per se has been shown to be nontoxic2) whereas its products OH and other radicals are the most powerful oxygen species known in living organisms'). Thus the aqueous solution of amino acids formed a variety of products when exposed to ionizing radiation due to the presence of oxidizing species, whereas UV light was much less destructive both in terms of number and variety of degradation products'). Rapid photodegradation of thiobencarb') and phenylalanine6) in the presence of hydrogen peroxide has been reported. The present communication describes the effect of UV light on aqueous solutions of citrulline in the presence of hydrogen peroxide. The ultraviolet source was a 125 W medium pressure mercury arc bulb with out glass envelope (Philips, India), which emits predominantly at 254 nm. Aque ous solutions of citrulline, adjusted to pH 7.0, were exposed to the UV light as described earlier'). The concentration of hydrogen peroxide was 50 mM unless mentioned otherwise. Ion exchange chromatography on Dowex 50W-X8 resin') was the basic method used in the separation of citrulline-hydrogen peroxide photoproducts. The details of the procedure has been reported earlier'). Amino acids were estimated with the modified ninhydrin reagent'). Ammonia was deter mined with Nessler's reagent as described earlier"). For the estimation of urea, the solution was incubated with urease') and the ammonia liberated was esti mated with diacetyl monoxime"). Absorbance was read at 470 nm for urea and 490 nm in case of citrulline. Fig. 1. Dowex 50W-X8 chromatography on a long column of the photoproducts from citrulline in a hydrogen peroxide solution. Seven ml aqueous solution of citrulline (5 mM) containing hydrogen peroxide (50 mM) were irradiated with UV light for two hours. The products were chromatographed on a Dowex 50W-X8 column of 0.9 cm x 100 cm length, under the conditions described in the figure. The peaks identified from left to right are …