KINETIC AND STRUCTURAL PROPERTIES OF CASSAVA RUBP CARBOXYLASES

Abstract

In this study, the kinetic properties of RuBP carboxylases of 16 cassava cultivars and the structural properties of their purified enzymes were investigated. Since cassava RuBP carboxylase has not been studied before, the buffer conditions for the extraction of an active enzyme preparation as well as the conditions for the maximum activation of the enzyme were also determined. Successful extraction of the cassava enzyme was accomplished with 100 mM Bicine-NaOH pH 8, 25 mM MgCl2, 5 mM DTT and 1 % (w/v) PVP-1 0. Maximum activation of the enzyme was achieved within 3 min with 5 mM Mg2+ and 100 mM HCOa- at 25°c. Kinetic studies revealed the existence of natural variability in the kinetic parameters of the enzyme from the different cultivars. Structural studies also demonstrated the existence of structural variability in the subunits of the carboxylases in terms of their amino acid compositions, tryptic peptide mapping patterns and serological relationships.