| Abstract
| - Site-directed mutagenesis has been used to probe the role of Arg172 in ascorbate utilizationby ascorbate peroxidase. Arg172 was changed to lysine, glutamine, and asparagine. Although each ofthese variants retains the ability to utilize guaiacol as a reductant, they exhibit large decreases in theirsteady-state rates of ascorbate utilization. Spectroscopic, steady-state, and transient-state experiments indicatethat these variant proteins are capable of reacting with hydrogen peroxide to form Compound I, but theirability to oxidize ascorbate to form Compound II, and subsequently the resting state, is severely impeded.Results are presented which highlight the importance of Arg172, and a model is proposed to explain itsrole in ascorbate utilization.
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