Distribution of calmodulin-stimulated ca transport into membrane vesicles from green spinach leaves

A microsomal fraction isolated from green spinach leaves exhibited a Mg(2+) and ATP-dependent (45)Ca(2+) uptake. Addition of 10 micromolar carbonyl cyanide m-chlorophenylhydrazine had no effect. The cationophore A23187 (10 micromolar) induced the release of (45)Ca(2+) accumulated by membrane vesicles. Membranes prepared from lower epidermis showed the highest Ca(2+) accumulation activity. Microsomal fractions from petiole, lamina, and midrib were less active. The stimulation by bovine brain calmodulin was about 30% for the lower epidermis, 23.5% for midrib, and below 20% for petiole and lamina.