THERMAL-DENATURATION AND GELATION OF RUBISCO - EFFECTS OF PH AND IONS

In order to understand the mechanism of thermal gelation of rubisco, i ts native and heat denatured states were characterized by absorbance, fluorescence and circular dichroism spectroscopies as well as by diffe rential scanning calorimetry in the presence of various salts. It appe ars that during the denaturation process, divalent anions are released while divalent cations are fixed by the protein, while it is disorgan ized and while the environment of its aromatic chromophores becomes mo re hydrophilic. The pH transition of gelation is shifted 1-2 pH units higher than the transition of denaturation temperature which occurs ne ar the isoelectric point of the native molecule. This shift probably c orresponds to the breaking of saline bridges within the protein molecu le. Finally, a large effect of divalent cations on the phase diagram i ndicates that a particular denatured state is attained when these cati ons are in the denaturation medium. Copyright (C) 1996 Elsevier Scienc e B.V.