Abstract— U.V. irradiation of trans‐urocanic acid frozen in an ice matrix results in trans, trans, trans‐2,4‐di‐imidazolyl‐1,3‐cyclobutanedicarboxylic acid from pH 8.0 solutions; or cis, trans, cis‐3, 4‐di‐imidazolyl‐1, 2‐cyclobutanedicarboxylic acid from pH 5.9 solutions.
THE RESIDUES remaining from acid extracts of white guinea pig epidermal homogenates prepared in a blender were observed to fluoresce orange-red under ultraviolet light (u.v.). The fluor was extractable from the keratin mass by ethanoVHC1 (70: 30, v/v) and was detectable under either long (360 nm) or short (254 nm) U.V. illumination when a drop of the concentrated extract was applied to filter paper. When exposed to air, the fluorescence disappeared within a few days. It was also promptly destroyed by alkali.Quantitative analysis showed that these extracts, exhibiting fluorescence on filter paper, contained several times as much copper as would be present normally in the total epidermal preparation. Epidermal homogenates prepared in an all glass apparatus showed orange-red fluorescence only after the addition of a few p g of copper sulfate. This suggested that the orange-red fluorescence was dependent upon small amounts of exogenous copper. The traces of copper necessary for production of the fluor initially observed were found to have been derived from the interaction of the metal parts of the Waring blender with the acid medium during homogenization.Treatment of epidermal homogenates, free of exogenous copper, with pepsin at pH 2.0 released a functional group which reacted with copper sulfate to form the orange fluor. Gradual release of a copper-dependent orange fluor could be demonstrated when a drop of the supernatent was applied to filter paper, lightly sprayed with CuSO, (2 X M), air dried and illuminated with U.V. The capacity for emitting copper-dependent orange fluorescence from the keratin mass slowly decreased during the course of enzymic digestion and was not detectable after 36 hr (1.0 mg pepsin/50g epidermis, 30°C). These observations suggested that the functional group reacting with copper to form a fluor could be either a peptide or an amino acid.A study of individual amino acids in v i m showed that a solution of cysteine applied to filter paper and sprayed lightly with dilute copper sulfate solution fluoresced orange under U.V. Thin layer chromatography indicated that the fluor liberated from epidermis could be cysteine. Red fluorescence has been reported previously when propyl-thiouracil was evaporated to dryness on glass in the presence of copper salts [ 11.Cysteine cuprous mercaptide was prepared anaerobicly from Cu,O employing procedures described by Hopkins [2]. The white cuprous mercaptide precipitate showed weak orange fluorescence in the flask when illuminated with 360nm light. The fluorescence was intensified upon drying the precipitate. The precipitate contained 28.61 2 0.20% CU.
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