GTP-specific pyrophosphorylation of thiamin in dark-grown soybean (Glycine max) seedling axes |
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Authors: | Patrick K. W. Howle Roger C. Fites |
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Affiliation: | USDA-ARS, 411 Borlaug Hall, Univ. of Minnesota, 1991 Upper Buford Circle, St Paul, MN 55108, USA;Dept of Botany, Box 7612, North Carolina State Univ., Raleigh, NC 27695-7612, USA. |
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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 m M ), GTP was the preferred nucleotide with an apparent Km of 0.021 m M . 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. |
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Keywords: | Glycine max GTP product inhibition soybean thiamin pyrophosphate thiamin pyrophosphotransferase |
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