Structural basis of cation exchange, complex formation and redox properties in chloragosomes

Components of chloragosomes isolated from Octolasium transpadanum ROSA were separated by fractional extraction. The chemical composition of the fractions was determined and their effect on the anion- and cation-binding capability and on the lipophilic property of chloragosomes was studied. The acid-alcoholic extract of chloragosomes contained, among others, metalloporphyrins with 2 or 4 free -COOH groups; the residuum consisted of basic proteins. The metalloporphyrins and phosphatides gained by extraction with chloroform-methanol neutralize the basic groups of the chloragosome proteins, thus, an excess of free acidic groups develops, which is responsible for the polyanionic nature and cation exchange of chloragosomes. The apolar groups of phosphatides and carotenoids are responsible for the lipophilic nature of chloragosomes. Under experimental circumstances both in vivo and in vitro, organic cations were bound to chloragosomes, partially by a cation-exchange mechanism and partially by formation of more stable complexes. A small amount of anions may be absorbed by the bound cations. The diluted acidic extract of chloragosomes predominantly contain organic cations, in the present study riboflavin, flavin nucle0tide and thiamine were determined. Chloragosomes, owing to their structure, form complexes of varying stability with anions, cations and hydrophilic compounds equally. This feature explains their capability of cumulating trophic and toxic substances, while their redox activity is explained by their metalloporphyrin, flavin, thiamine and carotene content.