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
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