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THE EFFECT OF pH ON RAPESEED GLOBULIN (CRUCIFERIN) BINDING TO ANILINONAPHTHALENE‐8‐SULFONATE
Author(s) -
APENTEN RICHARD K. OWUSU,
FOLAWIYO YETUNDE L.
Publication year - 1995
Publication title -
journal of food biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 47
eISSN - 1745-4514
pISSN - 0145-8884
DOI - 10.1111/j.1745-4514.1995.tb00548.x
Subject(s) - chemistry , fluorescence , titration , dissociation constant , mole , sulfonate , chromatography , biochemistry , inorganic chemistry , receptor , sodium , physics , organic chemistry , quantum mechanics
The fluorescence emission intensity from rapeseed globulin (cruciferin) increased in the presence of anilinonaphthalene‐8‐sulfonate (ANS) at pH 2.0 but not at pH 10. Fluorescence titration studies showed that at pH 7 cruciferin binds 22 (±0.6) moles of ANS per mole of protein with an average dissociation constant (K d ) of 1.9 (±0.1) × 10 −5 M. At pH 2.0 the number of ligand binding sites (n) decreased to 14 (±0.2) moles of ANS bound per mole of cruciferin. However, the ANS binding affinity increased by about five times (K d = 3.6 (±1.1) × 10 −6 M). The fluorescence emission spectrum maxima (Λ max ) for the cruciferin‐ANS complex showed a blue shift at pH 2 when compared to Λ max values at pH 7–10. These results are consistent with a loss of the quaternary and tertiary structures of cruciferin and the exposure of surface hydrophobic ANS binding sites at low pH. Cruciferin‐ANS binding parameters at pH 10 were not significantly different from values at pH 7; n = 22 and K d = 2.7 (±0.2) × 10 −5 M. Based on these ANS fluorescence measurements cruciferin is stable under alkaline conditions.