Acid and Neutral Invertases in the Mesocarp of Developing Muskmelon (Cucumis melo L. cv Prince) Fruit

Abstract

Acid and neutral invertases were found in the mesocarp of developing muskmelon (Cucumis melo L. cv Prince) fruit and the activities of these enzymes declined with maturation of the fruit, concomitantly with the accumulation of sucrose. Neutral invertase was only present in the soluble fraction and acid invertase was present in both the soluble and cell-wall fractions. The cell-wall fraction contained three types of acid invertase: a NaCl-released invertase; an EDTA-released invertase, and a tightly bound invertase that still remained on the cell wall after treatment with NaCl and EDTA. The soluble acid and neutral invertases could be separated from one another by chromatography on DEAE-cellulose and they exhibited clear differences in their properties, namely, in their pH optima, substrate specificity, K(m) values for sucrose, and inhibition by metal ions. The EDTA-released invertase and the soluble acid invertase were similar with regard to their chromatographic behavior on DEAE-cellulose, but the NaCl-released invertase was different because it was adsorbed to a column of CM-cellulose. The soluble acid invertase and two cell-wall bound invertases had very similar characteristics with regard to optimal pH and temperature, K(m) value for sucrose, and substrate specificity.