ISSN:
1365-3040
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Abstract. Purified acid phosphatase from sycamore cell walls is not activated by increasing the ionic strength of the reaction mixture. However activation occurs when the enzyme is bound to small cell wall fragments. The apparent activation of the bound enzyme by ions is paralleled by a decline of the substrate concentration C1/2, that results in half of the maximum rate. Above ionic strengths of about 0.05 the bound and solubilized enzyme forms behave in the same manner. Titration of cell wall fragments at different ionic strengths show that the local pH, inside the cell wall fragments, is lower than the pH in bulk solution. These results are explained in the light of poly-electrolyte theory. The negative charges of the cell walls generate an electrostatic potential that results in the attraction or repulsion of ions. The local concentration of organic phosphate (the substrate of the enzyme) is then lower than its concentration in bulk solution. This concentration difference explains that the value of C1/2, or of the apparent Km of the bound enzyme, is greater than the true Km of the solubilized enzyme. Increasing the ionic strength tends to equalize bulk and local ion concentrations, and therefore apparently activates the bound enzyme.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/1365-3040.ep11581782
