The effect of 1-ethyl-3(3-dimethylaminopropyl)carbodiimide on calcium binding and associated changes in chloroplast structure and chlorophyll a fluorescence in spinach chloroplasts.

1. Chemical modification of carboxyl groups on the chloroplast membrane with a water-soluble carbodiimide plus a nucleophile caused inhibition of Ca-2plus binding. 2. Both binding sites were affected and showed a decrease in the number of binding sites and an increase in the dissociation constant. 3. Cation-induced changes in chlorophyll a fluorescence and structural changes (deltaA540) were inhibited at the same carbodiimide concentrations as Ca-2plus binding, emphasizing the relationship between these processes. 4. Chloroplasts that were illuminated with high intensity light for short time periods showed a decrease in the carbodiimide-mediated inhibition of Ca-2plus binding.