Identification of the Porphyrin Compound Found in Cultures of C. diphtheriæ and mycobacteriæ.

Porphyrin was found by the present authors 1 in bouillon cultures of C. diphtheriæ, in amounts which vary with the toxicity or flocculative titer of the filtrates. Other investigators 2 - 6 have confirmed the occurrence of this pigment in C. diphtheriæ filtrates, by observations made both in the visible and in the ultraviolet spectrum. We have found a pigment, apparently identical, in Old Tuberculin, and in fluid cultures of several species of Mycobacteria. The chemical composition of the pigment, however, has remained in doubt. Its absorption-spectrum is that of a hemochromogen or metal-porphyrin compound. In ethereal extracts sharp bands are found in the visible at 574 and 538 mμ, and in the near ultraviolet an intense absorption with its maximum at 407.9mμ. The pigment shows an oxidation-reduction change, the oxidized form being colorless. When extracts are treated with strong mineral acid the pigment breaks down, and there appears free coproporphyrin and the copper compound of this substance.

In the effort to identify the pigment we undertook the synthesis∗ of compounds of coproporphyrin with a number of metallic radicles: Fe, Mg, Mn, Co, Ni, Cu, Sn, and Zn. After an interruption this work has been resumed under more favorable conditions. Of the various metallic compounds studied, only those of Cu, Fe, and Zn are of present significance.

The Zn compound is formed readily when a solution of zinc salt is added to coproporphyrin in slightly alkaline aqueous solution. The combination is stable over a rather wide pH range but is disrupted by strong mineral acid. The absorption-spectra in various solvents are very similar.

In ethereal solution sharp bands are present about μ 574 and 539; one of greater intensity is found at μ 407.8. In aqueous solution the pigment exhibits an oxidation-reduction change, the oxidized form king colorless.