Characterization of thiamin-binding protein from maize seeds

A thiamin-binding protein (TBP) was isolated from maize (Tripsacum zea) seeds. It was estimated to have a molecular mass of 96 kDa, and consist of two 46-kDa subunits. The protein contained a large amount of glutamine or glutamic acid (14.4 mol%) and glycine (10.6 mol%). The levels of methionine (0.1 mol%) and tryptophan (0.6 mol%) in the protein were low. The optimum pH for its thiamin-binding activity was 8.0. It bound free thiamin specifically, not thiamin phosphates. The apparent dissociation and maximum bound values for thiamin-binding were 0.42 μM and 22.2 nmol·mg–1 protein, respectively. These properties of thiamin-binding protein from maize seeds were similar to those of the thiamin-binding protein from rice seeds, not from buckwheat, sesame, sunflower or spruce seeds. Also, the TBP from maize seeds had immunological homology with the TBP from rice seeds, but not the other plant seed TBPs. Further, it was accumulated only in the seeds in the same manner as TBP of rice seeds.