Common Molecular Features among Amaranth Storage Proteins

Abstract

The structure of albumin 2 protein fraction of amaranth was investigated. It was formed by several major polypeptide subunits of molecular masses of 52.3 ± 0.8, 54 ± 2, and 56 ± 1 kDa. The former and the latter subunits were composed of a peptide of molecular mass between 31 and 38 kDa linked by S−S bonds with another peptide of molecular mass between 19 and 23 kDa. The 54 kDa subunit together with the 31−38 and 19−23 kDa subunits formed S−S-linked aggregated polypeptides. Lyophilized albumin 2 was highly polymerized, having a complex monomer component with a molecular mass of 300 ± 10 kDa. The polymers were partially stabilized by SS linkages. Because of these structural characteristics, albumin 2 was very similar to amarantin except for the presence of the 54 kDa subunit and its tendency to polymerize. Two components were obtained by gel filtration of globulin fraction. The major one exhibited heterogeneity of species and showed some common features with albumin 2. The minor component eluted at a lower volume and also showed heterogeneity, with a main species of 7S and a minor one of 12S. Their major peptides had molecular masses of 78, 72, 39, 30, and 20 kDa similar to the 7S type globulin. Its size, larger than that of amarantin, is different from a 7S type globulin, but the possibility of becoming polymerized or having a shape quite different from that of a sphere cannot be dismissed. Keywords: Amaranth; globulin; albumin 2; protein structure; gel filtration; electrophoresis

Physicochemical and structural properties of amaranth protein isolates treated with high pressure

“…Table 2 depicts the denaturation temperatures and enthalpies (T d y ΔH d ) of amaranth protein isolates in either native state (0.1 MPa) or treated with HP (200, 400 and 600 MPa) at different protein concentrations (1%, 5% and 10%). The native isolate exhibited the two characteristic endotherms, one at 70.7°C with an enthalpy of 4.1 J g − 1 that can be attributed to the denaturation of albumins and a minor globulin fraction (globulin-7S), and a second one at 98.6°C with an enthalpy of 5.7 J g − 1 corresponding to the denaturation of the protein fractions globulin-11S, globulin-P and glutenins (Avanza & Añón, 2007;Martínez et al, 1997).…”

“…The polypeptide composition of samples was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) using a separating gel (12% w/v in polyacrylamide) with a stacking gel (4% w/v in polyacrylamide) in a minislabs system (Bio-Rad Mini-Protean II Model) (Martínez, Castellani, & Añón, 1997). The following continuous buffers system were used: 0.375 mol L − 1 Tris-HCl, 1 g L − 1 SDS, pH 8.8, for the separating gel; 0.025 mol L − 1 Tris-HCl, 0.192 mol L − 1 glycine and 1 g L − 1 SDS, pH 8.3, for the running buffer; and 0.125 mol L − 1 Tris-HCl, 200 ml L − 1 glycerol, 10 g L − 1 SDS, 0.5 g L − 1 bromophenol blue (p.a., Sigma Chemical Co.), pH 6.8, as sample buffer.…”

Amaranth proteins as a source of antioxidant peptides: Effect of proteolysis

“…There was a significant presence of peptides with molecular mass lower than 10 kDa in Is (about a 78% of the total protein mass), including very small peptides (about a 3.5% of the total protein mass) ( Table 5). The polypeptide composition of the Is fraction cannot be compared with those currently described for amaranth isolates (Martinez & Añón, 1996, Martínez, Castellani and Añón 1997, Scilingo, Molina-Ortiz, Martínez and Añón, 2002 because it contains only proteins and polypeptides soluble in phosphate buffer at pH 7.8.…”

Seed protein characterisation of eleven species of amaranthus

“…Así, las fracciones mayoritarias constituidas por proteínas de peso molecular altos fueron de 300 kDa (fracción A), alrededor de 180 kDa (fracción B), 120 kDa (fracción C), entre 40 y 50 kDa (fracción D), entre 20 y 30 kDa (fracción E) y otras por debajo de 10 kDa (fracciones F, G y H). Se ha descrito la presencia en las semillas de amaranto de una proteína de reserva semejante a la legumina de las leguminosas con un peso mayor de 300 kDa y denominada amarantina (Martinez et al, 1997). Esta proteína tiene la …”

“…Por un lado un grupo bien definido entre 50 y 64 kDa. Se ha sugerido que estos péptidos pueden representar una forma inmadura de subunidades α−β componentes de la amarantina que, por causas desconocidas, no se disocia en los péptidos α y β tras el tratamiento con β-mercaptoetanol (Martinez et al, 1997). Otro grupo de péptidos está constituido por moléculas con un peso entre 33 y 37 kDa.…”