Alternate substrates of dopamine beta-hydroxylase. I. Kinetic investigations of benzyl cyanides as substrates and inhibitors.

摘要: Abstract A series of benzyl cyanide analogs have been studied as substrates and inhibitors dopamine beta-hydroxylase to extend our initial report (Baldoni, J. M., Villafranca, (1980) Biol. Chem. 255, 8987-8990) which showed that p-hydroxybenzyl was a suicide substrate beta-hydroxylase. Thus, the appVmax values for decrease in order p-OH greater than m-OH H much p-OCH3,m-OCH3; m-OH, m-OCH3 p-OCH3 are competitive versus tyramine velocity studies. The Vmax nearly identical at saturating O2 ascorbate (pH 5.0, 37 degrees C) but Km is 0.14 2.8 mM, respectively, with cyanide. Studies pH dependence log V/K show two pKa 5.2 5.8 while m-hydroxybenzyl 5.3 5.9. profile shows one 5.9 substrate. enzymic groups involved binding and/or catalysis these substrates. All inactivators With cyanide, partition between inactivation (kcat/kinact) changed from approximately 600 17 varied 5.0 6.7. kinact value 6.0, suggesting an group must be deprotonated maximal inactivation. Copper essential by cyanides kinetic studies partially inhibited (approximately 50%) inactive enzyme molecules were completely inactive. following papers this discuss partial reactivation suicide-inhibited stoichiometry analogs.