Binding protein for N-1-naphthylphthalamic acid (NPA), an auxin transport inhibitor, was studied by analysis of the effects of reactions which modify particular amino acid side chains upon their binding activity. Na2SO3, N-ethylmaleimide (NEM) and dithiobisnitrobenzoic acid all inhibited the specific binding of NPA to its binding protein from Acer pseudoplatanus L. cells. The presence of 10-6 M Na2SO3 in the binding assay reduced the affinity of the binding protein to NPA from Kd of 1.5 × 10-8 M to Kd of 2.1 × 10-8 M, while concentration of the binding protein was not significantly changed. When the same analysis was applied to NPA binding to the NEM-treated membrane particles, it was found that NEM inactivated binding without changing the affinity for NPA. This study revealed the importance of sulphydryl group(s) in the maintenance of NPA binding protein activity.

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Keywords Amino acid side chain, Auxin, Transport carrier
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Journal Biologia Plantarum
Xing, T, Hall, J.F. (J. F.), Barker, R.D.J. (R. D.J.), & Elliott, M.C. (M. C.). (1996). Sulphydryl groups in the maintenance of the activity of binding protein for N-1-naphthylphthalamic acid from Acer pseudoplatanus cells. Biologia Plantarum, 38(1), 47–51. doi:10.1007/BF02879632