title: Absence of a common intermediate pool among individual enzyme chains of the energy-conservation pathway in chloroplasts of Euglena gracilis.
abstract: Tri-n-butyltin chloride is a specific inhibitor that binds stoicheiometrically and irreversibly with the ATP-synthesizing sites of chloroplasts. Titration of Euglena chloroplasts with tri-n-butyltin chloride shows about six ATP-synthesizing sites per molecule of cytochrome c(552) or per 380 molecules of chlorophyll. This system was used to study the possibility of linkage between individual enzyme chains of the energy-conservation pathway or the possible existence of a common pool of an intermediate in this pathway. The inhibition of ATP synthesis by tri-n-butyltin chloride at low rates of electron transport (low light-intensities, NADP(+) or ferricyanide as electron acceptor) agrees with a kinetic model of two to four ATP-synthesizing sites per energy-conservation chain. At high rates of electron transport, however, the results occasionally agree with a model of 20 or more sites per chain. The results are interpreted as indicating the absence of a common intermediate pool, but the presence of a limited degree of linkage between individual chains. It also indicates the presence of two energy-conservation sites in these chloroplasts.
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D001665:Binding Sites; D002712:Chlorides / Q000494:pharmacology; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology* / Q000378:metabolism; D003580:Cytochromes / Q000378:metabolism; D004579:Electron Transport; D005055:Euglena / Q000201:enzymology* / Q000378:metabolism; D005292:Ferricyanides; D007700:Kinetics; D009249:NADP
chemical_list: D002712:Chlorides; D003580:Cytochromes; D005292:Ferricyanides; D002734:Chlorophyll; D009249:NADP; D000255:Adenosine Triphosphate