EXPLORING THE CATALYTIC MECHANISM OF SKELETAL-MUSCLE UDP-GLUCOSE PYROPHOSPHORYLASE - IDENTIFICATION OF A HYPERREACTIVE CYSTEINE AT THE ENZYME ACTIVE-SITE

1. The involvement of cysteine residues in the catalytic mechanism of UDP-glucose pyrophosphorylase was suggested by the rapid inactivation of the enzyme by N-ethylmaleimide, even at 1:1 reagent/enzyme stoichiometric ratios. 2. The inactivation is largely prevented by uridine substrates (UDP-glucose and UTP) in agreement with the assumption that the reactive cysteine is located at the active site.