Crystallization and partial characterization of dimethylallyl pyrophosphate: L-tryptophan dimethylallyltransferase from Claviceps sp. SD58.

Dimethylallyl pyrophosphate: L-tryptophan dimethylallyltransferase (dimethylallyl tryptophan synthetase) has been purified from Claviceps strain SD58 to a homogeneous crystalline form. The enzyme is pure as judged by polyacrylamide gel electrophoresis and contains two similar subunits of 34,000 molecular weight as shown by electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate. Since the enzyme was determined to have a molecular weight of 70,000 by gel exclusion chromatography, it is dimeric. The substrates dimethylallyl pyrophosphate and tryptophan each have mixed (negative to positive) cooperativity with a minimum Hill coefficient of 0.37 and 0.73, respectively. Calcium ion is a positive allosteric effector and, at 20 mM concentration, deregulates the enzyme. The deregulated enzyme has Km values of 7.2 microM for dimethylallyl pyrophosphate and 8.8 microM tryptophan. The Vmax under deregulated conditions is 953 nmol/min/mg, giving a turnover number of 14. Ca2+ has a S[0.5] of 4.5 mM. The kinetic mechanism is random sequential.