Amaranth Globulin Structure Modifications Induced by Enzymatic Proteolysis

Globulin-P was partially hydrolyzed with papain under specific conditions to study the resulting structural modifications. Under mild hydrolytic conditions, globulin-P polymers were cleaved to render their unitary constituents (280 kDa molecules). Under stronger hydrolytic conditions these unitary molecules were 13% smaller than those from nonhydrolyzed globulin. Moreover, these molecules remained assembled even though they contained degraded polypeptides. The monomeric (M) subunit and the A chains were preferentially cleaved under mild and intermediate hydrolytic conditions, whereas B chains remained with the same size. These results suggest that the M and A polypeptides might be located at an exposed site of the molecules resembling the structure of the legumins. The M subunit may be participating in the stabilization of globulin-P polymers, on the basis that these two species disappeared under the same hydrolytic conditions. Similar events such as those described in this paper might be taking place on globulin-P during germination of amaranth grain. Keywords: Amaranth; globulin; papain; protein structure; proteolysis