| Abstract: | A conserved histidine residue at position 331 of rat tyrosine hydroxylase was changed to glutamine by site-directed mutagenesis. The mutant enzyme, TOH-H331Q, was expressed in E. coli with a pET3b-based vector. The level of expression was far less than that of the wild-type enzyme; the best preparations were approximately 60% pure in TOH-H331Q, and represented only 0.01% by weight of the total protein. The H331Q mutant had markedly reduced activity, below the detection resolution of the assay. The mutant enzyme showed no response to free ferrous iron at concentrations up to 50-fold above saturating for the wild-type enzyme. |
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