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Electrophoretic Behaviour of i-Urobilin and Stercobilin


As the urobilinoid pigments i-urobilin and stercobilin are known to contain both basic and acidic groups, we have investigated their electro-phoretic behaviour—yet unstudied—at various pH values. Paper electrophoresis was performed at 120 V., in acetate buffer (a mixture of M/5 acetic acid–sodium acetate buffer and 0.9 per cent sodium chloride solution) in the pH. range less than 6.0, and barbital buffer (Michaelis sodium barbital-sodium acetate-hydrochloric acid buffer) at pH greater than 6.0; the positions of the coloured spots were observed directly during the procedure, but even minute quantities of urobilinoid pigments could be seen at the end of the run after spraying the papers with Schlesinger reagent (saturated zinc acetate solution in ethanol), and observing the green fluorescence in ultra-violet light. With the exception of the sharply defined pH. value of 4.41 at which both urobilinoid pigments became immobile in the electric field, they moved towards the cathode at pH less than 4.41 and toward the anode at pH. greater than this value, the direction of movement, which was the same for both pigments, being dependent only on the pH. However, the rate of movement of these materials differed at various pH. levels: thus in buffers around pH 5.0 and at pH less than 4.41 stercobilin migrated faster toward the anode or cathode, respectively, whereas at higher pH values (8.6) urobilin was found to move faster than stercobilin in the anode direction.

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  1. 1

    Lemberg, and Legge, “Hematin Compounds and Bile Pigments”, 138 (Interscience Pub., New York, 1949).

  2. 2

    Gray, “The Bile Pigments”, 36, 118 (Methuen and Co., Ltd., London, 1953).

  3. 3

    Birch, Chem. and Indust., 652 (1955).

  4. 4

    Gray, and Nicholson, Nature, 179, 264 (1957).

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