Hydrogen exchange of the glycyl radical of pyruvate formate-lyase is catalyzed by cysteine 419 - PubMed (original) (raw)

. 1995 Feb 28;34(8):2393-9.

doi: 10.1021/bi00008a001.

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Hydrogen exchange of the glycyl radical of pyruvate formate-lyase is catalyzed by cysteine 419

C V Parast et al. Biochemistry. 1995.

Abstract

Pyruvate formate-lyase (PFL) catalyzes the reversible conversion of CoA and pyruvate into acetyl-CoA and formate. Active enzyme contains a glycyl radical whose alpha-hydrogen undergoes rapid exchange with solvent (t1/2 approximately 5 min at 0 degree C). We have investigated this exchange using site-directed mutagenesis and mechanism-based inactivation. Mutation of the active-site cysteine 419 into a serine, which renders the enzyme catalytically inactive, abolishes alpha-hydrogen exchange in the radical. This suggests that the exchange process is not an intrinsic property of the glycyl radical but is a consequence of its interaction with cysteine 419. This residue is also demonstrated to be involved in the transfer of the radical to acetylphosphinate, a mechanism-based inactivator of the enzyme. In contrast, mutation of the other essential cysteine 418 to a serine has no effect on the hydrogen exchange or the transfer of the radical to acetylphosphinate. A mechanism for the hydrogen exchange catalyzed by cysteine 419 consistent with a redox role for this residue in the normal catalytic reaction is proposed.

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