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Thiols in Glycolysis: Effects of Cysteine Modification on Pyruvate Kinase Activity
Lain, Taylor K
Lain, Taylor K
Abstract
Pyruvate kinase (PK), the tenth enzyme in glycolysis, undergoes significant activity changes with thiol modification at cysteine residues. This research explored the extent of these activity changes and of cysteine labeling experienced by PK after direct thiol modification by hydrogen peroxide, Ellman’s reagent, hypochlorous acid, glutathione, and dansyl-labeled glutathione derivatives. Mixed reactions with thiol-modifying agents and the reducing agents dithiothreitol and tris(2-carboxyethyl)phosphine examined the reversibility of labeling and restoration of activity. Results of these studies confirmed that PK activity may be modulated by cellular redox conditions. They determined that some of the residues responsible for labeling were not involved in PK functionality and that different reagents had varying degrees of modifying power and selectivity for functionally-relevant or non-functionally-relevant cysteine residues. They also indicated that full in vitro activity and observable thiol reduction occurred in slightly oxidizing conditions. This implied that PK could “protect” itself against functionally-relevant thiol modification at low physiological oxidant concentrations, potentially through non-functionally-relevant cysteine residues and other amino acids, and structurally reorient itself at these concentrations for effective function. This may suggest other protective roles for PK as a buffer against oxidation of more sensitive cysteine-containing proteins, such as tubulin and GAPDH, or as a marker for high levels of cellular oxidative stress.
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2015-05-01
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Chemistry