SPECTROSCOPIC ANALYSIS OF BACTERIOCHLOROPHYLLS IN VITRO AND IN VIVO*

Abstract— Chromatophores from Rhodopseudonionas spheroides were treated with potassium iridic chloride so as to destroy the major complement of bacteriochlorophyll (BChl) without harming the photochemically active P870. A band at 802 mμ, attributed to a pigment P800, survived this treatment along with P870. Extraction of such chromatophores with a mixture of acetone and methanol removed the absorption bands of P800 and P870; a corresponding amount of BChl was found in the extract. The yield of BChl was too great to have been derived from either P800 or P870 alone; analysis of extinction cofficients and band areas of these pigments indicates that they are both specialized fornis of BChl, in a molecular ratio of 2P800:1P870. Bleaching of P870, without attenuation of the absorption band of P800, could be effected by adding potassium ferricyanide to the iridic chloride-treated chromatophores. Extraction of chromatophores in this condition gave a reduced yield of BChl, consistent with a 2:1 ratio of P800 to P870 under the assumption that the BChl in the extract was derived in this case from P800 alone. An absorption band at 600 mμ in iridic chloride-treated chromatophores, characteristic of BChl and ascribed to P800 and P870, is partly bleached and shifted to shoiter wavelengths upon illumination. This reversible effect, and a similar one near 375 mμ (corresponding to the Soret band maximum of BChl), has the combined attributes of the blue-shift of P800 and the bleaching of P870 seen in a spectrally resolved form near 800 and 865 mμ respectively. The 600 mμ band is bleached by about 30 per cent, again consistent with a ratio of 2P800:1P870. These data, in conjunction with information published elsewhere, support the view that two molecules of P800 and one of P870 are associated jointly with a photosynthetic reaction center. It was observed that the long wave absorption bands of BChl in vivo are sometimes narrower than the narrowest bands that have been observed for BChl in dilute organic solutions. Sharpness of these bands is most conspicuous in some forms absorbing near 800 mμ.