Total proteins and 11S protein fraction (helianthinin) of sunflower seed (Helianthus annuus L.) - effect of acetylation and succinylation.

Total proteins and the helianthinin (11S) fraction from sunflower seeds were chemically modified by acetylation and succinylation. Extent of acetylation was 12, 51, 52, or 56% for total proteins and 12, 36, 69, or 71% for helianthinin; extent of succinylation was 8, 21, 33, or 49% for total proteins and 10, 30, 44 or 61% for helianthinin. Extent of modification was monitored by the availability of free lysyl residues in the proteins. Effects of modification were studied by absorption/fluorescence and sedimentation velocity analysis. UV absorption max. shifted to higher wavelengths in total proteins and in helianthinin following modification; there was also an increase in absorbance at 260 nm as a function of increased chemical modification. The sedimentation velocity profile indicated dissociation of the proteins to low mol. wt. fraction (2S) through a 7S component. Dissociation occurred at low modification levels in both total proteins and in helianthinin. There was a gradual red shift and quenching in the fluorescence emission max. at higher modification levels indicating the denaturation of the proteins as a result of chemical modification. Thermal denaturation of modified proteins was studied. Changes in absorbance as a function of temp. indicated minor changes suggesting that the conformation of the proteins has already been altered to a significant extent by chemical modification. [From En summ.]