PhotosynthesisResearch 23: 119-130, 1990. © 1990 Kluwer AcademicPublishers.Printedin the Netherlands. Minireview Metabolism of 2-carboxyarabinitol 1-phosphate and regulation of ribulose- 1,5-bisphosphate carboxylase activity JEFFREY R. SEEMANN, JOHN KOBZA & BRANDON d. MOORE Department of Biochemistry, University of Nevada, Reno, Nevada 89557, USA Received 13 March 1989;accepted 12 April 1989 Key words: CA1P, CO2 fixation, enzyme regulation, photosynthesis, rubisco, RuBP carboxylase Abstract Metabolism of 2'-carboxy-D-arabinitol 1-phosphate (CA1P) is an important component in the light-depen- dent regulation of ribulose-l,5-bisphosphate carboxylase (Rubisco) activity and whole leaf photosynthetic CO2 assimilation in many species, and functions as one mechanism for regulating Rubisco activity when photosynthesis is light-limited. Species differ in their capacity to accumulate CA1P, ranging from those which can synthesize levels of this compound approaching or in excess of the Rubisco catalytic site concentration, to those which apparently lack the capacity for CA1P synthesis. CA1P is structurally related to the six carbon transition state intermediate of the carboxylation reaction and binds tightly to the carbamylated catalytic site of Rubisco, making that site unavailable for catalysis. Under steady-state, the concentration of CA1P in the leaf is highest at low photon flux density (PFD) or in the dark. Degradation of CA1P and recovery of Rubisco activity requires light and is stimulated by increasing PFD. The initial degradation reaction is catalyzed by an enzyme located in the chloroplast stroma, CA 1P phosphatase, which yields carboxyarabinitol (CA) and inorganic phosphate as its products. The pathway of CA metabolism in the plant remains to be determined. Synthesis of CA 1P occurs in the dark, and in Phaseolus vulgaris this process has been shown to be stimulated by low PFD. The pathway of CA1P synthesis and its relationship to the degradative pathway remains unknown at the present time. The discovery of the existence of this previously unknown carbon pathway in photosynthesis indicates that we still have much to learn concerning the regulation of Rubisco activity and photosynthesis. Abbreviations; CA - 2'-carboxy-D-arabinitot, CA1P - 2'-carboxy-D-arabinitol 1-phosphate, CABP - 2'- carboxy-D-arabinitol-l,5-bisphosphate (transition state analog), PFD - photon flux density, Pi - inorganic phosphate, Rubisco - ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), RuBP - ribulose-1,5- bisphosphate Introduction Light-dependent regulation of Rubisco activity in- volves a number of interrelated mechanisms (for review, see Woodrow and Berry 1988). The most well studied of these mechanisms is that involving the reversible carbamylation of a specific lysine residue in the catalytic site of Rubisco (Miziorko and Lorimer 1983). The percentage of car- bamylated catalytic sites is proportional to PFD in many species (e.g. Perchorowicz et al. 1981, see also Butz and Sharkey 1989), although not in all (Kobza and Seemann 1988). In species in which decar- bamylation occurs, the binding of RuBP to decar- bamylated catalytic sites also occurs in vivo under certain conditions (Brooks and Portis 1988, Kobza and Seemann 1988, Cardon and Mott 1989). Re- lease of this inhibitory RuBP from Rubisco, with subsequent carbamylation of the enzyme, is app- arently facilitated by a chloroplast protein, Rubis-