Fractionation of Monovalent Ion-Stimulated Nucleoside Triphosphatase Activity in Extracts of Petiolar Tissues3

Adenosine triphosphatase activity, present in extracts of isolatedphloem and xylem tissues of Heracleum mantegazzianum and thepetioles of Helianthus annuus, has been fractionated on 7 percent polyacrylamide gels into electrophoretically distinct enzymeswith different properties. Extracts of whole petioles containfour enzymes capable of hydrolysing ATP, phloem extracts possesstwo, and xylem, one. Enzyme I, common to all the extracts, showspreferential hydrolysis of nucleoside triphosphates and is stimulatedby monovalent cations. Enzyme II, of phloem and of petiole extracts,is a general phosphatase. Enzymes III and IV, of petiole extracts,are specific for nucleoside triphosphates but are unaffectedby monovalent cations. All four enzymes are markedly inhibitedby Mg²⁺. None of the enzymes is affected by ouabain or oligomycin.     

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

Adenosine triphosphatase activity has been studied in fractionatedextracts of isolated phloem and xylem tissues of Heracleum mantegazzianumSomm. et Lev. and of petioles of Helianthus annuus L. Enzymeactivity 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 activityby monovalent cations is increased in preparations which haveeither been derived from acetone powders or pre-treated withdithiothreitol or cysteine.