I 77 . the Cataphoretic Mobility of Visual Purple

THE photosensitive substancecontained -in the -rods of the eyes of ve#tebrates, visual purple, is a chromoprotein, i.e. a protein to which one or more chromophores are attached. Aqueous solutions of visual puirple are-decomposed by light to give an unstable compound "transient orange", which in turn bleaches thermally to "indicator yellow" [Lythgoe, 1937]. Indicator yellow may also be formed without the action of light. Such treatment as is known to bring about denaturation of proteins is effective in bleaching visual purple and producing indicator yellow, e.g. heating of the solution, addition of alkali, acid or organic solvents and violent shaking. Wald [1937] found that a yellow pigment can be extracted with organic solvents from solutions of indicator yellow; this was explained by assuming that bleaching involves rupture of the bond between the protein and the chromophore. The object of the present work was to determine the isoelectric point of visual purple and the change in its cataphoretic mobility on bleaching. A preliminary account of some of the experimental results has been given previously [Broda et al. 1939]. EXPERIMENTAL