ATP + D-ribulose 5-phosphate = ADP + D-ribulose 1,5-bisphosphate + H(+) Activated by NADH and inhibited by phosphoenolpyruvate. Carbohydrate biosynthesis; Calvin cycle. Homooctamer. Is not found in cells cultured chemoheterotrophically and only low levels of activities are found in those grown photoheterotrophically on oxidized organic acids. Belongs to the phosphoribulokinase family.