Effects of Multivalent Cations on Cell Wall-Associated Acid Phosphatase Activity

AUTOR(ES)

Tu, Shu-I

RESUMO

Primary cell walls, free from cytoplasmic contamination were prepared from corn (Zea mays L.) roots and potato (Solanum tuberosum) tubers. After EDTA treatment, the bound acid phosphatase activities were measured in the presence of various multivalent cations. Under the conditions of minimized Donnan effect and at pH 4.2, the bound enzyme activity of potato tuber cell walls (PCW) was stimulated by Cu2+, Mg2+, Zn2+, and Mn2+; unaffected by Ba2+, Cd2+, and Pb2+; and inhibited by Al3+. The bound acid phosphatase of PCW was stimulated by a low concentration but inhibited by a higher concentration of Hg2+. On the other hand, in the case of corn root cell walls (CCW), only inhibition of the bound acid phosphatase by Al3+ and Hg2+ was observed. Kinetic analyses revealed that PCW acid phosphatase exhibited a negative cooperativity under all employed experimental conditions except in the presence of Mg2+. In contrast, CCW acid phosphatase showed no cooperative behavior. The presence of Ca2+ significantly reduced the effects of Hg2+ or Al3+, but not Mg2+, to the bound cell wall acid phosphatases. The salt solubilized (free) acid phosphatases from both PCW and CCW were not affected by the presence of tested cations except for Hg2+ or Al3+ which caused a Ca2+-insensitive inhibition of the enzymes. The induced stimulation or inhibition of bound acid phosphatases was quantitatively related to cation binding in the cell wall structure.

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