EFFECT OF PH AND IONIC-STRENGTH ON THE HEAT-STABILITY OF RAPESEED 12SGLOBULIN (CRUCIFERIN) BY THE ANS FLUORESCENCE METHOD

The heat stability of rapeseed 12S globulin (cruciferin) was examined using 8-anilinonaphthalene-1-sulphonic acid (ANS) as a fluorescence pr obe. Heating cruciferin (0.06-0.3 mg ml(-1) in 10 mM glycyl-glycyl pip erizine buffer, pH 7.0, with 0.1-1.0 M NaCl) for 20 min increased its hydrophobicity as monitored by ANS fluorescence measurements. The mid- point temperature for the heat effect (T-m) increased linearly with in creasing solvent pH (T-m (degrees C) = 4.16 pH + 41 (mu = 0.1)) or sod ium chloride concentration (T-m (degrees C) = 14.7 [NaCl] + 71 (pH = 7 .0)). The range of T-m values for cruciferin was 45-96 degrees C. At 2 0 degrees C cruciferin was unstable at pH < 3.0 but relatively stable under alkaline conditions (pH 8-10). Though possessing an oligomeric s tructure, cruciferin appears to heat denature in accordance with the t wo-stage deactivation model for simple globular proteins.