Subchloroplastic localization of NAD kinase activity: evidence for a Ca2+, calmodulin-dependent activity at the envelope and for a Ca2+, calmodulin-independent activity in the stroma of pea chloroplasts

Chloroplasts were prepared from pea seedlings and tested for NAD kinase activity. More than half of a Ca²⁺, calmodulin-dependent activity and most of a Ca²⁺, calmodulin-independent activity of the homogenate were associated with chloroplasts. The Ca²⁺, calmodulin-dependent activity could be detected by adding Ca²⁺ and calmodulin to the incubation medium containing intact chloroplasts. This activity could not be separated from the chloroplasts by successive washes or by phase partition in aqueous two-polymer phase systems. After chloroplasts fractionation, the Ca²⁺, calmodulin-dependent NAD kinase activity was localized at the envelope, and the Ca²⁺, calmodulin-independent activity was recovered from the stroma. In view of these results and of a previous report [Simon (1982) Plant Cell Rep. 1, 119–122] the occurrence and presumed role of calmodulin in the chloroplast are discussed.