THE PHOTOCHEMICAL REACTIONS OF 1,3–DIMETHYLURACIL WITH 1–AMINOPROPANE AND POLY‐l‐LYSINE*

Abstract

Abstract— Irradiation of 1,3–dimethyluracil (DMU) in 1–aminopropane (AP) with u.v. light resulted in the formation of reduced and dimeric forms of DMU and adducts between DMU and AP. The formation of these compounds may be rationalized from the activation of either DMU or AP. Irradiation of DMU and poly‐l‐lysine in water with u.v. light resulted in the extensive binding of DMU to poly‐l‐lysine. The pyrimidine is probably attached to the ε‐carbon of the polypeptide at the 6–position. The biological implications of these studies are discussed.

Cross-Linking of Proteins to Nucleic Acids by Ultraviolet Light

“…It is possible that photoinduced reactions of uracil toward hydrocarbonlike side chains of amino acids will involve addition at both the 5 and 6 positions of the uracil ring. Reactivity at both of these positions has also been observed in the photoreactions of 1,3-DMU with I-aminopropane (Gorelic et al, 1972).…”

“…Sato et al (1971) found that the irradiation of uracil, thymine and their analogs in formic acid led to the production of the corresponding dihydro derivatives. Gorelic et al (1972) discovered that DMU was photohydrogenated in the presence of l-aminopropane, while Shetlar (1975c) found that DMT was photo hydrogenated by 2-aminopropane. It was shown by Reeve and Hopkins (1975) that thymine and uracil, irradiated in the presence of tryptophan at A > 300 nm, were hydrogenated.…”

“…Gorelic et al (1972) examined the wavelength dependence of the reaction and found that the relative distribution of DMU-containing products did not depend significantly on the spectral range of incident radiation. These workers suggested that at longer wavelengths (A > 254 nm) the excited DMU abstracted a hydrogen from AP, via an electron transfer intermediate.…”

“…However, no data have been presented that would favor or rule out any of these possibilities. At wavelengths shorter than 254 nm, AP begins to absorb appreciable amounts of light in the systems that Gorelic et al (1972) studied. Aminoalkyl radical generation from the direct absorption of energy by the amine could lead to additional pathways of product formation that do not depend on the excitation of DMU.…”

“…The only studies in which products have been isolated are those of Gorelic et al (1972), who studied the photochemical reactions of 1,3-dimethyluracil (DMU) with I-aminopropane (AP); AP can be regarded as an analog of the uncharged side chain of lysine. Four adducts were isolated and characterized by chemical and spectroscopic methods.…”