Ton T. Hai

Use of a vinyl phosphonate analog of ATP as a rotationally constrained probe of the C5′O5′ torsion angle in ATP complexed to methionine adenosyl transferase

Abstract An analog of adenosine 5′-triphosphate (ATP) was synthesized in which the C4′C5′OPα system is replaced by a trans C4′CHCHPα system. In the form of 1:1 complexes with Mg, this analog and its counterpart with a C4′CH2CH2Pα system were linear competitive inhibitors, with respect to MgATP, of the MAT-II (normal tissue) and MAT-T (hepatoma tissue) forms of rat ATP: l -methionine-S-adenosyltransferase (MAT); K m ( ATP ) K i values ranged from 0.4 to 2.4. 2′-Deoxy-ATP was a weak substrate, K m ( ATP ) K m = 0.035 , of MAT-II and a weak competitive inhibitor, K m ( ATP ) K i = 0.07 , of MAT-T. These findings, together with interactions of the MAT forms with other substrates and inhibitors, indicate that binding of ATP to these transferases is accompanied by little rotation about the C5′O5′ bond, and that C4′ and Pα are in a trans-type relationship in enzyme-bound ATP.