Tryptochrome : a Pigment Derived from Tryptophan

Abstract

WHEN 5 ml. of a very dilute (c. 0.05 per cent) solution of tryptophan in 60–80 per cent acetic acid is treated with a drop of 1 per cent aqueous potassium iodate, and warmed to boiling, a violet-pink colour develops, and an intense greenish-orange fluorescence. On dilution with two volumes of water, the pigment gradually separates, and can be extracted with isobutyl alcohol or with chloroform, in Which solvent it shows a strong absorption band at λ565–555 mμ, and a weak band.at λ520–515 mμ. Pigment formation requires a large excess of acetic acid, otherwise the mixture turns brown, and an iodo-tryptophan is precipitated, from which the pigment cannot be generated. The pigment is stable in acid solution, and both tint and fluorescence survive exposure to air and light for months.