. Biological structure and function; proceedings. Biochemistry; Cytology. 328 JAMES H. C. SMITH 18 for a glycine buffer extract (pH 9-5). Because of the irradiation necessary for measuring fluorescence polarization, the protochlorophyll is largely converted into chlorophyll, consequently, the fluorescence obtained is mostly irom chlorophyll. These values, 15 and 18, are lower than the value for chlorophyll in castor oil, 28-9. Three possibilities suggest them- selves to account for the lowered polarization: one, that the holochrome rotates more freely than chlorophyll immobilized in castor oil
. Biological structure and function; proceedings. Biochemistry; Cytology. 328 JAMES H. C. SMITH 18 for a glycine buffer extract (pH 9-5). Because of the irradiation necessary for measuring fluorescence polarization, the protochlorophyll is largely converted into chlorophyll, consequently, the fluorescence obtained is mostly irom chlorophyll. These values, 15 and 18, are lower than the value for chlorophyll in castor oil, 28-9. Three possibilities suggest them- selves to account for the lowered polarization: one, that the holochrome rotates more freely than chlorophyll immobilized in castor oil; two, that it transfers its energy to other chlorophyll molecules; or three, that the pigment is free to rotate within the holochrome. Because the holochrome is so large, it cannot conceivably rotate fast enough to depolarize its fluorescence. The second suggestion of energy. 0-4 08 1-2 Chlorophyll absorbance Fig. 2. The reciprocal of the fluorescence polarization of the protochlorophyll- chlorophyll holochrome plotted against the optical density of the chlorophyll maximum (~ 670 m^u) at different stages of greening. transfer between chlorophyll molecules also seems improbable in view of the small number of pigment molecules per holochromatic particle. This leaves only the third alternative as likely. An estimate of the limiting fluorescence polarization value when no energy transfer exists can be obtained by extrapolating the fluorescence to zero pigment concentration. This was done by extracting the holochrome from leaves at different stages of greening, and by relating the fluorescence polarization with chlorophyll content through the expression i/P = iIPo + ACt (8) in which P is the polarization of fluorescence measured; A is a constant; C is the optical density of the chlorophyll peak at about 670 rufx, which is proportional to the chlorophyll content; r is the lifetime of the activated state; and Pq is the polarization when C is zero. A plot of ijP against. Please note t
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