Dissociation and denaturation behaviour of sesame-alpha-globulin in sodium dodecyl sulphate solution.

The effect ofanionic detergent, sodium dodecyl sulphate, on the majorprotein, alpha-globulin
ofsesame seed(Sesamum indicum L.) has been investigated by geljiltration, sedimentation
re!ocity, vi,rcosity, optical rotation, difference spectra and jluoresceuce measurements.
The detergem causes dissociation of the protein first and then denaturation.
In the deTergent concentration range of 1.75-4.0 x 10 - ~ M foul' components are
observed in the ultracentrifuge. The specific rotation ofthe protein increases with the
detergent concentration above 2.5 x 10 M and shows a cooperative transition
between 3-8 x 10 M detergent suggesting conformational change; above 8 x 10 M
detergent The value of - [alpha] does not change. The reduced viscosity nred however,
increases above 2.5 x 10- 3 M detergent and does not attain a plateau value. The
difference spectrum ofthe protein indicates that both tryptophan and tyrosine groups
have been affected by the detergent. The fluorescence intensity decreases and the
maxima shifts towards red in the detergent solution resulting in an 'isoemissive point'
at 355 nm. The double difference spectra in sucrose-detergent protein system show that
below 5·0 x 10- 3 M detergent, the difference absorption andjluorescence spectrum result
from the binding of the detergent near the chromophoric groups and are not due to
conformational change. Binding studies by equilibrium dialysis indicate the presence
of ~ 50 binding sites in the protein and a binding constant of 3.0 x 103