Antenna Activity of Metal-Substituted Chl a Bound to the Chl a-Binding Sites in PS1 RC Complexes

Abstract

The antenna-depleted PS1 complexes with a Chl a/P700 ratio of 12 were used for reconstitution of antenna activities. Zn-Chl a bound to the complexes both with the binding affinity and the antenna activity as high as Chl a. The same results were obtained with Cd-Chl a, except that it had a binding affinity as half as Chl a. Hg-Chl a bound to the Chl a-binding sites with the same binding affinity as Chl a, but without any antenna activity, probably due to the lifetime of its excited state too short to transfer its excitation energy to the neighboring Chl. Cu-Chl a, as well as Phe a, bound to the complex, but with the formation of aggregated forms and without any antenna activities, suggesting that Cu-Chl a could bind not to the Chl a-binding sites, but probably on the protein surface.