Stimulation by Monovalent Cations of Adenosine Triphosphatase Activity in Extracts of Petiole Tissues3

Abstract
Adenosine triphosphatase activity has been studied in fractionated extracts of isolated phloem and xylem tissues of Heracleum mantegazzianum Somm. et Lev. and of petioles of Helianthus annuus L. Enzyme activity in the microsomal fraction is maximal with ATP as substrate. Monovalent cations stimulate activity, but only below pH 7·0. Divalent cations are inhibitory. Stimulation of ATPase activity by monovalent cations is increased in preparations which have either been derived from acetone powders or pre-treated with dithiothreitol or cysteine.

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