Lysine 2,3-Aminomutase: Rapid Mix−Freeze−Quench Electron Paramagnetic Resonance Studies Establishing the Kinetic Competence of a Substrate-Based Radical Intermediate

Publisher Website
Google Scholar
Abstract
Lysine 2,3-aminomutase from Clostridia catalyzes the interconversion of l-lysine and l-β-lysine. The enzyme contains iron−sulfur clusters and is activated by pyridoxal 5‘-phosphate and S-adenosylmethionine, all of which participate in catalysis. Current spectroscopic evidence implicates two substrate-based organic radicals as intermediates in the mechanism. One of these species, the radical N3-(5‘-phosphopyridoxylidene)-β-lysin-2-yl (3), appears in the steady state of the reaction of lysine and has been definitively characterized by EPR and ESEEM spectroscopy. The 2-deuterio form of this radical, 3-2-d, which is generated in the reaction of l-[2-2H]lysine, can be distinguished by line shape analysis from 3. The rate at which the signal for 3-2-d is transformed into that for 3 has been measured by rapid mix−freeze quench kinetic analysis. The rate constant for this process is 24 ± 8 s-1 at 21 °C. This is the rate constant for the turnover of radical 3 and is indistinguishable from the turnover number of lysine 2,3-aminomutase. Therefore, radical 3 is kinetically competent as an intermediate in the reaction of lysine 2,3-aminomutase.

This publication has 3 references indexed in Scilit: