Based on our own and other researchers' experimental data, a model of the light-induced assembly of Calvin cycle enzymes on the membranes of stromal thylakoids is suggested. According to this model, the components involved are: (1) the photosystem I chlorophyll–protein complex containing the P700 reaction center, which possesses a stroma-exposed and pH-dependent carbohydrate-binding site performing both photo- and chemoreceptor functions, and (2) ribulose-1,5-bisphosphate carboxylase (Rubisco), a glycoenzyme, which is a specific ligand of the lectin in the stromal thylakoids. After stroma alkalization in light, the carbohydrate-binding site of the photosystem I pigment–lectin complex is transformed into an active state, and this transformation increases the enzyme carboxylase activity.