PARENT SESSION
Posters P1A Proton coupled electron transport and ATPase. Abstracts (172-180)

The principle of redox regulation of chloroplast ATPase activity. Toru Hisabori^{*,1, 2}, Hanayo Ueoka-Nakanishi^{1, 2}, Yoichi Nakanishi^{1, 2, 3}, Dirk Bald^{1, 4}, Ken Motohashi^{1, 2}, Masasuke Yoshida^{1, 2}, Hiroki Konno^{1, 2}, ¹ Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan² ATP System Project, ERATO, JST, Yokohama, Kanagawa, Japan³ Lab. Cell Dynamics, Grad. Sch. Bioagr. Sci., Nagoya Univ., Naogya, Aichi, Japan⁴ Dept. Struct. Biol. Free Univ. Amsterdam, Amsterdam, The Netherlands

ABSTRACT- The enzyme activity of ATP synthase of chloroplast (CF₁) from higher plants and green algae is highly regulated by several ways, such as activation by a proton gradient across the membranes, inhibition by a product ADP, and activation by reduction of a disulfide bond on the subunit of the enzyme complex. The redox-dependent regulation of the enzyme activity is only observed on CF₁ but not on the other ATP synthase. In vivo the reduction of is achieved by electrons supplied from the photosystem via thioredoxin. The structural basis for this redox regulation is assigned to the special portion of the subunit including two cysteine residues. This portion resides only in the subunit of the redox-sensitive ATP synthase. Although the activities of the various enzymes are regulated by thioredoxin in chloroplasts, not very much is known about the molecular mechanism of redox regulation of these enzymes so far. Due to the lack of the three dimensional structure information of the regulatory region of CF₁-, we still cannot figure out the molecular mechanism of redox regulation of CF₁. By using the redox-sensitive chimeric complex of thermophilic bacterial F₁-ATPase, in which the regulatory region of the subunit of redox-sensitive CF₁ was genetically introduced, we succeeded in observing the redox regulation of rotation of the subunit. The detailed analysis of the regulated rotation revealed that the suppressed enzyme activity of the oxidized form complex was characterized by more frequent prolonged pauses during rotation. The molecular mechanism of the redox regulation of ATP synthase, which enables to control the rotation behavior, will be discussed.

KEY WORDS: ATP synthase, rotation, CF1, thioredoxin