Purification and characterization of GDP-D-mannose 4,6-dehydratase from porcine thyroid.

The enzyme GDP-D-mannose 4,6-dehydratase has been purified 1500-fold from porcine thyroid tissue. The enzyme exhibits a molecular mass of 251000 Da as determined by sedimentation techniques. Its subunit size was determined as 41500 Da by dodecyl sulfate gel electrophoresis. The enzyme has a Km of 3.3 microM with respect to GDP-D-mannose and appears specific with respect to this substrate. The enzyme appears to be inhibited by guanine nucleotides and by guanine nucleotide sugars. It is particularly susceptible to inhibition by GDP-L-fucose. It is suggested that this compound may have a physiological function as an end-product feedback inhibitor.