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

Abstract

Chloroplasts were prepared from pea seedlings and tested for NAD kinase activity. More than half of a Ca 2+ , calmodulin‐dependent activity and most of a Ca 2+ , calmodulin‐independent activity of the homogenate were associated with chloroplasts. The Ca 2+ , calmodulin‐dependent activity could be detected by adding Ca 2+ 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 Ca 2+ , calmodulin‐dependent NAD kinase activity was localized at the envelope, and the Ca 2+ , 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.