PHYSICAL AND CHEMICAL PROPERTIES — PROTOCHLOROPHYLL HOLOCHROME 335 



INFLUENCE OF PH ON THE SPECTRAL ABSORPTION OF PROTO- 

 CHLOROPHYLL IN THE HOLOCHROME 



If alkalinity affects the association of protochlorophyll with protein, 

 the absorption spectrum of protochlorophyll in the holochrome should 

 vary with pH. This deduction comes from the fact that the absorption 

 spectra of protochlorophyll in the free and holochromatic states differ. 



The absorption spectrum of protochlorophyll does vary with pH. It 

 shifts to shorter wavelengths with higher pH as the results of Table I show. 

 This is what would be expected if dissociation were greater at higher 

 alkalinities. 



TABLE I 



Effect of pH Values on the Absorption Maximum 

 OF Protochlorophyll Holochrome 



DISRUPTION OF THE CYCLOPENTANONE RING 



When protochlorophyll holochrome is treated at alkalinities near pH 1 1, 

 the absorption spectrum of the protochlorophyll changes drastically in the 

 blue region of the spectrum. The absorption band at 421 m/z is increased 

 in height at the expense of the 440 m^u. band. The spectrum obtained, 

 Fig. 8, is similar to that obtained by Granick [16] for protoporphyrin and 

 magnesium protoporphyrm (cf. insert Fig. 8), which indicates the con- 

 version of pheoporphyrin to porphyrin. Whether this disruption of the 

 cyclopentanone ring takes place before or after the splitting of the pigment- 

 protein complex is being examined at the present time. 



Summary 



Measurements on the fluorescence polarization of protochlorophyll 

 holochrome have led to the supposition that protochlorophyll is attached 

 to amino acid "tails" of the protein in the holochrome. This supposition 

 has been strengthened by determinations on the inhibition of the trans- 

 formation by alkali. The results of these determinations indicate the 

 involvement of several amino acids in this pigment-protein binding. 

 Comparison of the pH values effective in preventing the transformation 



