PHYSICAL AND CHEMICAL PROPERTIES — PROTOCHLOROPHYLL HOLOCHROME 327 



the protochlorophyll conversion since the amount of chlorophyll formed 

 by illumination was found to be statistically related molecule-for-molecule 

 to the carotenoid present [3]. Now that we have found the carotenoid 

 fraction to be made up of several constituents it would be necessary to 

 assume that each constituent was equally effective in the conversion of 

 protochlorophyll in order to account for the stoicheiometry of the reaction. 

 This is very unlikely, and militates against such an hypothesis. A further 

 argument against such an assumption is that in etiolated albino leaves 

 nearly complete conversion occurs in the absence of carotenoids [3]. It is 

 improbable, therefore, that carotenoids are involved in the protochloro- 

 phyll transformation. 



It has frequently been proposed that carotenoids function as inhibitors 

 of the photo-oxidation of chlorophyll. The isolated carotenoid-containing 

 holochrome, however, loses its chlorophyll by extended illumination. In 

 this system, little protection against bleaching is afforded by the presence 

 of yellow pigments. 



Fluorescence polarization of protochlorophyll holochrome 



When the fluorescence of a molecule is excited with plane polarized 

 monochromatic light, the fluorescence emitted under certain circum- 

 stances may also be partly polarized. In principle, if a fluorescing molecule 

 remains stationary and retains its absorbed energy during the interval 

 between absorption of the exciting light and emission of the fiuorescence, 

 it emits fluorescence having a certain maximum degree of polarization. 

 Polarization values lower than this indicate that the molecule has either 

 rotated or else transferred its energy to like molecules during the period of 

 excitation [5, 6]. Much can be learned about the state of fluorescent sub- 

 stances from measurement of this property. Because of this, the fluorescent 

 properties of the protochlorophyll holochrome have been studied by this 

 technique [7, 8]. 



The fluorescence polarization of the protochlorophyll holochrome was 

 measured in an apparatus similar to that used previously by Goedheer [5]. 

 To test the operation of the apparatus, the fluorescence polarization of 

 chlorophyll in castor oil was determined. The value, 28-9, was found 

 which agrees well with Goedheer's former measurement, viz. 28. Light 

 from the cadmium arc, wavelength 644 m/z, was used for exciting the 

 fluorescence. 



Preliminary experiments in collaboration with Dr. Paul Latimer [7] 

 gave polarization of fluorescence values for protochlorophyll holochrome 

 lower than for chlorophyll in castor oil. This observation was corroborated 

 by Goedheer and Smith [9], who obtained a value of 15 for a glycerine 

 extract of protochlorophyll holochrome from etiolated bean leaves, and 



