ScienceAsia 13 (1987): 133-157 |doi: 10.2306/scienceasia1513-1874.1987.13.133

STRUCTURE, FUNCTI0N, AND REGULATION OF RIBULOSE-1, 5-BISPHOSPHATE CARBOXYLASE/OXYGENASE

ARAN INCHAROENSAKDI^a,b AND TETSUKO TAKABE^a

ABSTRACT: Ribulose-1, 5-bisphosphate carboxylase/oxygenase is a key enzyme in photosynthesis. The structure of the enzyme in both prokaryotes and eukaryotes consists of eight pairs each of large subunits (A) and small subunits (B) with the quaternary structure AsBa. The only exception is that found in a photosynthetic bacterium Rhodospirillum rubrum which has the structute A₂ Subunit A is the site of catalytic activity for both carboxylase and oxygenase. Subunit B is also essential for the manifestation of both activities and its partial role is to stabilize the activated form of the enzyme. The biosynthesis of the enzYme in higher plants requires the participation of both chloroplast and nucleus. Subunit A is encoded by chloroplast DNA whereas subunit B is encoded by nuclear DNA. The assembly process of the two subunits is not well understood at present. Regulation of the enzyme activity is mainly mediated by light which causes an increase in pH in the chloroplast, optimalfor enzyme activity, as well as an increase in magnesium concentration. Changes in the level of a phosphate ester inhibitor, 2-carboxyarabinitol-l-phosphate, as affected by light can also regulate the enzyme activity. Recent studies have shown the presence of a new protein, RuBisCO activase, which is responsible for the regulation of the enzyme in vivo. Light also regulates the synthesis of the enzyme. The synthesis of subunit A is light-regulated at the post-transcriptional level, whereas the synthesis of subunit B is regulated at the level of transcription. With recent developments in recombinant DNA technology, the possibility exists of altering the reactivity of the enzyme towards either substrate, C0₂ or 0₂. However, so far such attempts by using site-specific mutagenesis have not proved successful yet.

Download PDF

a Research Institute for Biochemical Regulation, School of Agriculture, Nagoya University, Chikusa, Nagoya 464, Japan.
b Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10500, Thailand.

Received 14 March 1987