MIANS is a particularly convenient probe because it is
essentially nonfluorescent until the maleimide moiety reacts
covalently with a Cys residue (43), when a time-dependent
increase in fluorescence is observed. At a low MIANSLacY
ratio, the increase in fluorescence is due primarily to reaction
with Cys-148, as shown by mass spectrometry (44), and the
reaction is inhibited as a function of substrate concentration.