Effect of Method of Preparation on the States of Chlorophyll in Euglena Chloroplast Fragments as Determined by Fluorescence Spectroscopy

The state of chlorophyll in chloroplast fragments is affected by such factors as the ionic strength and pH of the suspending medium. With increasing ionic strength or at pH values other than neutrality, there is a decrease in the fluorescence yield of the form of chlorophyll with fluorescence maximum at 715 to 736 mmu (aggregate) and an increase in the yield of the form with fluorescence maximum at 685 mmu (monomer). (Positions of maxima cited are for 77 degrees K.) These changes in yield are accompanied by modifications in absorption and fluorescence excitation spectra. It is also noted that these effects are similar to the ones brought about by pancreatic lipase, wheat germ lipase, pancreatic trypsin or urea. An interpretation is given which is consistent with the experimental data, namely, that the effects originate in conformational changes in the proteins to which the pigments are attached. These conformational changes give rise to an increase in the size of the aggregate and a decrease in the probability of energy transfer between the monomer and aggregates.