Rubisco activase Background Information The Calvin cycle uses ATP and NADPH generated by the light reactions of photosynthesis to reduce carbon dioxide to sugar (1). The enzyme that catalyzes the first step in the Calvin cycle is ribulose bis-phosphate carboxylase (designated Rubisco) (1). Rubisco activase is a nuclear encoded protein that is transported to the chloroplasts where it catalyzes the activation of Rubisco (2,3). The Arabidopsis Rubisco activase gene, which is located on chromosome 2, encodes mRNA that undergoes alternative splicing to yield two forms of Rubisco activase protein (3,4). Rubisco activase is expressed throughout the green parts of the plant, but not in roots or petals (5). Rubisco activase protein content accounts for approximately 5% of the total soluble protein in the green plant tissue (5). Expression of Rubisco activase is regulated by light, carbon-dioxide and a circadian clock (5-7).
