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English: Spectroscopic data on P750 in Anacystis nidulans. (A) Absorbance spectra of two different concentrations of suspensions of A. nidulans cells showing the presence of a band in the 750–760 nm range (called P750; modified and reproduced from Govindjee et al., 1961). (B) Excitation spectra of fluorescence of P750 (measured at its red-most end, at 810 nm) of A. nidulans at 77 K (−196°C) and at 293 K (20°C). A portion of excitation spectrum of the green alga Chlorella is reproduced (open triangles) to show the absence of the excitation band at 750 nm. A curve for MgO is shown (open squares) to point out that the rising part of the curve beyond 760 nm is an artifact due to scattering (reproduced from Govindjee, 1963b).