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Glutathione peroxidase —
the cost of
keeping the peace.
A molecule is only half the story; the other half is the machinery that works on it. This new chapter turns to the enzymes of glutathione, and it begins with the one that spends it — glutathione peroxidase, the enzyme that draws on the tripeptide to reduce peroxides, and that carries a rare element at its active site.
I
The enzyme that spends glutathione —
and the chapter of machinery it opens.
This series has spent a long time on glutathione the molecule — what it is built from, how it cycles, the company it keeps. But a molecule does little on its own. Around glutathione sits a set of enzymes — protein machines that build it, use it, and recycle it — and this chapter turns to them. It is fitting to begin with the enzyme that puts glutathione to work, because it is the reason the cell keeps such a large supply of the tripeptide in the first place: glutathione peroxidase, the enzyme that spends it.
The job glutathione peroxidase performs is, in chemical terms, a reduction. Cells continually produce peroxides — hydrogen peroxide and related compounds — as ordinary by-products of their metabolism. Glutathione peroxidase, often shortened to GPx, catalyses a reaction in which these peroxides are reduced to water or to simple alcohols, and the cost of that reaction is paid in glutathione. Two molecules of reduced glutathione are drawn in and joined together into the oxidised form, GSSG, in the course of the reaction. The enzyme is, in effect, the point in the cell where glutathione is converted from its reduced to its oxidised state in service of handling peroxides.
This places glutathione peroxidase on the consuming side of the cycle that the article on GSH and GSSG described. That earlier piece mapped the cycle as a loop between two forms; glutathione peroxidase is one of the enzymes that turns the loop, spending reduced glutathione on one side. The enzyme that pays it back — glutathione reductase — is the subject of the next article in this chapter. Together they keep the cycle running.
A molecule is only half the story.
The other half is the machinery.
Glutathione peroxidase is the enzyme
that puts the tripeptide to work.
The four parts of the enzyme
Four elements of glutathione peroxidase —
the substrate, the reaction, the active site, and the family.
Glutathione peroxidase can be understood through four parts. The cards below sketch each — what it draws on, what it does, what sits at its centre, and how many forms it takes.
I
The substrate
Reduced glutathione (GSH)
The enzyme draws on reduced glutathione as its source of electrons. Two molecules of GSH are consumed in each turn of the reaction and joined into the oxidised form, GSSG. Glutathione is, in this sense, the fuel the enzyme spends.
II
The reaction
Reducing peroxides
The enzyme catalyses the reduction of hydrogen peroxide to water, and of lipid peroxides to their corresponding alcohols. It is a chemical reduction reaction — the conversion of one molecule into another by the transfer of electrons.
III
Selenocysteine
The active site
At the heart of most forms of the enzyme sits selenocysteine — a version of the amino acid cysteine in which a selenium atom takes the place of sulphur. This rare amino acid is what makes glutathione peroxidase a selenium enzyme.
IV
The family
Several isoforms
Glutathione peroxidase is not a single protein but a family of related enzymes, several of them selenium-dependent, found in different parts of the body and the cell — the cytosol, the membranes, the gut, the bloodstream. A set, not a singleton.
II
The selenium at the centre —
why a rare element sits in the active site.
The most distinctive feature of glutathione peroxidase is the element at its core. Most enzymes are built entirely from the ordinary twenty amino acids, but glutathione peroxidase, in most of its forms, carries selenocysteine — an amino acid in which a selenium atom occupies the position that sulphur holds in ordinary cysteine. Selenocysteine is sometimes called the twenty-first amino acid, and it is incorporated into proteins by a special piece of cellular machinery reserved for the purpose. Glutathione peroxidase is among the most prominent of the proteins that use it.
This is the point where two threads of the series tie together. The article on selenium and the glutathione cycle described how a rare trace element found its place in this chemistry; glutathione peroxidase is the enzyme that place runs through. The selenium an organism takes in is used, among other things, to build the selenocysteine that sits at the active site of this enzyme. It is a neat illustration of how the cell's chemistry connects: a trace element in the diet, an unusual amino acid, and an enzyme that draws on glutathione, all meeting at a single point.
Why selenium rather than sulphur? The chemistry of selenium makes the active site especially well suited to the particular reaction the enzyme carries out, a difference of reactivity between the two related elements that biochemists have studied in detail. The series has already followed sulphur through much of glutathione's story; selenium is its rarer cousin in the periodic table, sitting one row below, and glutathione peroxidase is the clearest example of the cell putting that cousin to specific use.
Sulphur runs through glutathione's story.
Selenium is its rarer cousin —
and glutathione peroxidase
is where the cell puts it to use.
The enzyme in numbers
Three observations on glutathione peroxidase —
the cost, the element, and the family.
Two GSH
Two molecules of reduced glutathione are drawn in for each turn of the reaction
The enzyme spends glutathione two molecules at a time, joining them into the oxidised form GSSG as it reduces a peroxide. This is the consuming side of the GSH and GSSG cycle, the point where reduced glutathione is converted to oxidised.
One selenium
A single selenium atom, carried in selenocysteine, sits at the active site of most forms
Selenocysteine — cysteine with selenium in place of sulphur — sits at the heart of the selenium-dependent forms of the enzyme. It is what makes glutathione peroxidase one of the body's most prominent selenium-using proteins.
Several forms
A family of related isoforms, distributed across different tissues and cellular compartments
Glutathione peroxidase is a family rather than a single enzyme, with isoforms found in the cytosol, the membranes, the gut, and the bloodstream. Each occupies its own location, and several carry the selenocysteine active site.
III
The enzyme in the machinery —
one half of a turning cycle.
Glutathione peroxidase makes most sense when seen as one half of a pair. On its own, it would run the cell's reduced glutathione down, converting it steadily into the oxidised form as it handles peroxides. What keeps the supply from being exhausted is a second enzyme, glutathione reductase, which runs the reaction the other way — rebuilding reduced glutathione from the oxidised form, drawing on the cell's reducing power to do so. Between the two enzymes, glutathione cycles continuously between its reduced and oxidised states, and the pool is maintained. Glutathione peroxidase spends; glutathione reductase rebuilds. The next article in this chapter takes up the second of the pair.
This pairing is the first glimpse of the larger machinery this chapter will map. Glutathione is surrounded not by one enzyme but by a whole set — the enzymes that synthesise it from its amino acids, the enzymes that attach it to other molecules, the enzymes at the cell's edge that take it apart for recycling. Glutathione peroxidase is simply the most direct illustration of why the machinery exists at all: the cell maintains a large supply of glutathione precisely so that enzymes like this one have it on hand to spend. The literature on the glutathione peroxidase family is extensive and still developing, with research continuing on its many isoforms and their distribution across tissues.
Within the Codeage catalogue, the cellular pillar is built around the molecule these enzymes act upon. The Liposomal Glutathione formulation supplies the tripeptide itself; the combination formulas, from Liposomal Glutathione+ to the Liposomal Vitamin C+ Platinum, bring several related molecules together in single liposomal formats. These sit within the Pillar 03 architecture of the Longevity Code, where the molecules of cellular chemistry are housed as one coherent daily system. The literature on glutathione peroxidase continues to develop; the picture described here reflects the current understanding rather than a closed account.
Codeage · Cellular Longevity · Pillar 03
The molecule the enzymes act upon —
formats from the Pillar 03 line.
The tripeptide at the centre of the enzyme machinery — formulations from the Codeage glutathione line, in formats designed for daily use.
Liposomal Glutathione
The cornerstone of the Codeage glutathione line. Reduced L-glutathione (GSH) supplied in a phospholipid vesicle format — the Helix Liposomal format used in select Codeage formulations. The Pillar 03 anchor of the cellular redox conversation.
View Product →Liposomal Glutathione+
A combination liposomal format pairing reduced L-glutathione with CoQ10 and vitamin C — three molecules the literature has explored in the context of cellular redox biology, brought together in the Helix Liposomal vesicle architecture.
View Product →Liposomal Vitamin C+ Platinum
A liposomal vitamin C formulation built with L-glutathione, NAC, resveratrol, and rutin — molecules the literature has examined in connection with cellular redox biology, assembled in a single Helix Liposomal preparation.
View Product →Previously in this series
The Cellular Antioxidant Neighborhood — Glutathione Among the Molecules
Codeage · The Longevity Code
The molecule and its machinery —
within one daily system.
The cellular pillar of the Longevity Code houses the tripeptide at the centre of its enzyme machinery as part of one coherent daily architecture.
Explore The Longevity Code →This article is provided for educational and informational purposes only and has been reviewed against FDA and FTC guidelines to ensure it does not make any health, disease, or treatment claim. Any research or studies referenced were conducted independently and did not involve Codeage products; no Codeage product has been used in any study or to establish, prove, or imply any benefit. These statements have not been evaluated by the Food and Drug Administration. Codeage products are not intended to diagnose, treat, cure, or prevent any disease.
