Different possibilities for the formation of complexes of copper and zinc with chlorophyll inside photosynthetic organelles: Chloroplasts and thylakoids

Abstract

The possibility of the formation of copper and zinc complexes with chlorophyll in photosynthetic organelles (chloroplasts) and suborganelles (thylakoids) was studied. The visible and fluorescence spectra obtained from chloroplasts and thylakoids in the presence of the two metals confirmed complex formation in the case of copper, while such possibility appears to be very minor in the case of zinc. The reason for this distinction lies in the different type of complexes which chlorophyll forms with the two metals: only "central" or "substitution" copper-chlorophyll complexes may be formed inside the two isolated entities, while the formation of a possible zinc-chlorophyll "peripheral" type of complex is prevented for steric reasons. The latter fact is of high biological relevance, since both complexes may cause an irreversible impairment and damage of photosynthetic function.