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

摘要

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.