Invertase From Leaves of Phaseolus vulgaris Plants Grown on Nutrient Solutions Containing NaCl

Abstract

Two invertases occur in leaves of P. vulgaris with pH optima near 5.0 and 7.5. They have been separated and partially purified by chromatography on DEAE-cellulose. Tris-HCl buffer at 10 mM inhibited the former enzyme by only 7% but the latter enzyme by 90%. A comparison of the enzymes from leaves of plants grown on 0, 20 and 50 mM NaCl in nutrient solution showed that the amount of the pH 5.0 enzyme was significantly lower in the NaCl treatments, whereas the amount of the pH 7.5 enzyme was not shown to be significantly affected by the salt treatment. The K_m values for sucrose were about 7.5 and 27 mM for the partially purified pH 5.0 and pH 7.5 enzymes respectively, and they were not altered by NaCl treatment of the plants. A previous report of NaCl causing increasing K_m values for sucrose at pH 5.0 in less pure extracts [Hawker and Walker (1978) Aust. J. Plant Physiol. 5, 73-80] was presumably an artefact, possibly caused by interference by the pH 7.5 enzyme or by other unknown reactions.