Calmodulin Activation of Plant Microsomal Ca2+ Uptake

The active ATP-dependent uptake of Ca²⁺ into a plasma membrane-enriched microsomal fraction from plants is stimulated by the addition of plant as well as bovine brain calmodulin. This stimulation occurs only when the microsomes are prepared in the presence of EDTA. Plant calmodulin also activates the bovine brain 3‧,5‧-cyclic-nucleotide phosphodiesterase (EC 3.1.4.17). Mitochondrial Ca²⁺ accumulation is not affected by calmodulin. The calmodulin-mediated activation of microsomal Ca²⁺ uptake is abolished by the antipsychotic drug fluphenazine, whereas the calmodulin-independent Ca²⁺ uptake is only slightly decreased.