GTP‐specific pyrophosphorylation of thiamin in dark‐grown soybean (Glycine max) seedling axes

Abstract

ATP:thiamin pyrophosphotransferase (TPT: EC 2.7.6.2) was purified 5 900‐fold from 48 h dark‐grown soybean [Glycine max (L.), Merr. cv. Ransom II] seedling axes. TPT activity was monitored during purification by measuring the formation of thiamin pyrophosphate (TPP) from [2‐14C]‐thiamin at optimal pH (7.3). Although other nucleoside triophosphates were active as pyrophosphate donors (apparent Kms from 21 to 138 mM), GTP was the preferred nucleotide with an apparent Km of 0.021 mM. TPT activity was extremely sensitive to TPP formation, suggesting product feedback inhibition of TPT activity in vivo. Sulfhydryl, H+ and Mg2+ concentrations, either independently or in concert, were found to affect TPT activity.

Seed Storage Protein, Functional Diversity and Association with Allergy

“…These proteins are found in metabolically inactive and unphosphorylated forms [94]. During germination, thiamine phosphate synthases and thiamine pyrophosphokinase convert thiamine into thiamine pyrophosphate [95][96][97]. Thus, thiamine phosphate synthase regulates the total amount of thiamine during germination.…”