Kinetic analysis of light-dependent exchange of adenine nucleotide on chloroplast coupling factor CF1 Academic Article uri icon


  • 1. Introduction Chloroplast coupling factor CF, contains tightly bound ADP which is exchanged against added ADP only on energization of the thylakoid membranes [l-6]. This ADP binding site is probably different from the catalytic ADP binding site in the process of photophosphorylation [S-9]. Nevertheless it may be involved in the mechanism of energy transduction. Light-induced nucleotide exchange and photophos- phorylation show a parallel behavior in their depen- dence on several external factors, e.g., light intensity, pH,uncoupling and electron transport inhibition [lo]. The mechanism of ADP exchange involves two consecutive reversible reactions and three different forms of CFI which can be characterized by different states of the ADP binding site [ 111: (i) A stable CF1 -ADP complex (tightly-bound ADP); (ii) An unstable transitory CFl-‘ADP complex (loosely bound ADP); (iii) A metastable dissociated complex containing an unoccupied ADP binding site. The energy-requiring step is thought to be related to a conformational change of the protein by which tightly bound ADP is transferred to the loosely bound form. The loosely bound ADP molecule can be replaced by dissociation and re-association with a free ADP molecule. The latter reaction does not require an energized state of the membrane [ 111. During illumination of the chloroplasts all three forms *

publication date

  • June 1, 1979