Soluble and wall-bound invertases in strawberry fruit

Abstract

The relationship between the changes in soluble neutral sugar content and the changes in the activities of soluble and wall-bound invertases was investigated at various stages throughout the development of strawberry ( Fragaria × ananassa Duch. var. Hókowase) fruits. Glucose, fructose and sucrose concentrations were relatively low at the immature stage and, thereafter increased during development. The two hexose sugar concentrations were substantially higher than the sucrose concentration at all stages. Soluble acid invertase activity increased parallel to the accumulation of hexose sugars. In contrast, the activities of two types of wall-bound invertase (the NaCl-released and ethylenediaminetetraacetic acid (EDTA)-released ones) were relatively high at the immature stage and then declined steadily during the ripening of the fruit. Soluble and wall bound invertases exhibited similar enzymological properties with regard to optimal pH and temperature, the K m-value forsucrose and the substrate specificity. However, they exhibited different degrees of inhibition by Ag +, Hg 2+ and Mn 2+ ions.