Substrate binding order in mevalonate 5-diphosphate decarboxylase from chicken liver.

The substrate binding order of chicken liver mevalonate 5-diphosphate decarboxylase was investigated by using competitive inhibitors of the substrates. Mevalonate and mevalonate 5-phosphate showed mixed inhibition when ATP was the varied substrate. Both analogues of ATP, adenosine 5'-O-(3-thiotriphosphate) and beta-tau methylene adenosine 5'-triphosphate showed uncompetitive inhibition against mevalonate 5-diphosphate. These results are in accordance with an ordered sequential mechanism with mevalonate 5-diphosphate as the first substrate to bind to the enzyme.