Abstract
The mechanism of sucrose transport and the influence of various concentrations of sulfite on its activity was studied in the mesophyll vacuoles isolated from cottonwood (<em>Populus deltoides</em> Bartr. ex Marsh) leaves. Kinetic analysis of [<sup>14</sup>C] sucrose uptake by isolated vacuoles revealed the presence of a saturable component with K<sub>m</sub> for sucrose uptake = 23 mM and Vmax = 21.2 nmol sucrose 10<sup>-6</sup> vacuoles min<sup>-1</sup>. The saturable component was inhibited by SH-blocker, p-chloromercuribenzenesulfonic acid (PCMBS) and was substrate specific. The transport of sucrose was not changed by ATP with or without Mg<sup>2+</sup>, by the ionophore, valinomycin and by protonophores, carbonylcyanide m-chlorophenyl hydrazone (CCCP) or dinitrophenol (DNP). Sulfite at concentrations of 0.01-2.5 mM inhibited the uptake of [<sup>14</sup>C] sucrose by isolated vacuoles. Inhibition was of the noncompetitive type with K; = 2.48 mM of sulfite (22<sup>o</sup>C).
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