On the Topochemistry of the Active Site of Bovine Liver Monoamine Oxidase B PDF

Keywords

bovine liver, fluorescence, electron spin

Abstract

Fluorescence and electron spin (spin labelling) resonance spectroscopy were used to verify the nature of the active site of bovine liver monoamine oxidase B. Fluorescence polarization studies demonstrated that the flavin moiety moves with a certain degree of mobility around the covalent bond. The ESR spectrum of the enzyme labelled with an N-ethylmaleimide spin label shows components corresponding to weakly and to strongly irrunobilized labels. The binding of the probe to the active site over a temperature range of 5-50°C was studied. From the change of the ESR spectra, it is suggested that the active enzyme is in thermal equilibrium between two conformational states, and this conformational change involves only a short region of the active site of the enzyme. It is also suggested that the two conformational states may involve not only the active site suUhydryl group, but also the environment surrounding the flavine moiety of the enzyme. A model of the two conformational states of the active site of the enzyme is proposed.