Jul 27, 1976

Binding of phosphorylcholine to an IgM Waldenström as studied by fluorescence spectroscopy and circular dichroism

W F RiesenJ C Jaton


The binding characteristics of an IgM Waldenström(FR) for the ligand phosphorylcholine has been studied by fluorescence spectroscopy. Upon phosphorylcholine addition, IgM FR exhibited 83% enhancement of the tryptophanyl fluorescence, which was associated with a red shift of the emission maximun (5nm). The same properties were observed with the 7S IgM subunits. The association constant KA for phosphorylcholine was 6X10(4) M-1 FOR IgM FR and the 7S subunit, as determined by fluorescence titration, a value in agreement with the obtained by equilibrium dialysis. No significant decrease in the KA value was found in the presence of 3 M urea; in 6 M urea, the increase in fluorescence intensity was 36% of the value obtained in the absence of denaturing agent. In contrast, only 4% of fluorescence enhancement was noted upon binding in 3 M GuHC1 and no enhancement could be seen when the concentration of GuHC1 was increased to 5 M, thus suggesting complete unfolding of the protein and subsequent loss of binding activity. The pH dependence study of the phosphorylcholine binding to IgM FR indicated no significant differences in the fluorescence enhancement between pH 5 and 8, whereas at more acidic or alkaline pH values, the enhancement bec...Continue Reading

Mentioned in this Paper

Fluorescence Spectroscopy
Plasma Protein Binding Capacity
Urea Measurement
Circular Dichroism, Vibrational

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