A protein-protochlorophyll complex obtained from inner seed coats of Cucurbita pepo. The resolution of its two pigment groups into true protochlorophyll and a pigment related to bacterial protochlorophyll.

1. The inner seed coats of Cucurbita pepo were extracted with aqueous acetone and found to contain pigments with spectra similar to that of protochlorophyll. 2. When the fruits of C. pepo were stored the amount of protochlorophyll-like material in the inner seed coats increased and a form of protochlorophyll absorbing at longer wavelength was apparently formed. 3. The pigment was resolved into two forms of protochlorophyll by chromatography on sugar columns. One form with absorption maxima in ether at 432, 535, 571 and 623mmu was spectroscopically identical with plant protochlorophyll; the other, with absorption maxima at 438, 537, 574 and 624mmu, was spectroscopically identical with bacterial protochlorophyll isolated from the tan mutant of Rhodopseudomonas spheroides. The two phaeoporphyrins obtained from the seed-coat pigments closely resemble the corresponding phaeoporphyrin derivatives of plant protochlorophyll and bacterial protochlorophyll in spectroscopic and partition properties. 4. The pigment in the cells of inner seed coat of C. pepo is concentrated in discrete particles of about 1.7mu diameter. Extracts of the seed coats in a glycerol-glycine buffer were similar in spectroscopic properties to the crude protochlorophyll holochrome, but were not light-transformable. 5. After partial purification of the glycerol-glycine buffer extracts a pigment-protein complex was obtained with absorption maxima at considerably longer wavelengths than in organic solvents. 6. Preparations of the seed-coat protochlorophyll, in the presence of bovine serum albumin, adsorbed on filter paper or in colloidal solution, did not have absorption bands shifted so far to the red region as the natural protein complex isolated from the seed coat. 7. It is suggested that bacterial protochlorophyll (magnesium 2,4-divinylphaeoporphyrin a(5) methyl ester) is involved in the biosynthesis of chlorophyll in both plants and photosynthetic bacteria.