DMAT synthetase

Fig. 4. Incorporation of C-amino acids into DMAT synthetase and other proteins in 4-day old tryptophan-induced cultures of Clavlceps strain SD58 (A) 3 hr...

It is a monomeric protein of M.W. about 70,000, shows Kj, values for L-tryptophan and dimethylallyl pyrophosphate of 0.067 and 0.2 mM, respectively, and seems to have a relatively low turnover number, about 7 sec . During studies on this enzyme it was observed (13) that agroclavlne and elymoclavine, the terminal alkaloids in the strain used for the isolation of the enzyme, inhibited purified DMAT synthetase. At concentrations of 3 mM ( v<750 mg/1) agroclavlne and elymoclavine inhibited the enzyme 90% and 70%, respectively. The inhibition is of a mixed or uncompetitive type as shown by kinetic analysis with either tryptophan or dimethylallyl pyrophosphate as the variable substrate (Fig. 6). Subsequently, feedback Inhibition by elymoclavine was also demonstrated by GrSger s group (3) for chanoclavlne cyclase and by us for anthranllate synthetase from... 

The biosynthesis of ergot alkaloids is initiated by prenyla-tion of tryptophan with dimethylallyl pyrophosphate (DMAPP) to yield 4-dimethylallyltryptophane (DMAT) (4) (Fig. 35.2) (Floss, 1980). This alkylation step is believed to be rate limiting, and the enzyme that catalyzes this reaction, DMAT synthetase, has been purified more than 60 times (Maier and Groger, 1976 Waller and Dermer, 1981). The enzyme appears to be specific for L-tryptophan and is inhibited by agroclavine (2) and elymoclavine (5) the end products of the reaction. 

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