SOD (Superoxide Dismutase).

SOD converts superoxide into hydrogen peroxide, which is itself a reactive species. Catalase breaks that peroxide down to water and oxygen, so the two enzymes complete one continuous clearance step.

Glutathione peroxidase uses reduced glutathione to remove the hydrogen peroxide that SOD generates. Adequate glutathione keeps the second half of the pathway moving at the same rate as the first.

Glutathione peroxidase is a selenoenzyme, so selenium status sets how fast the peroxide produced by SOD is cleared. Low selenium leaves that downstream step as the slow point.

The cytosolic and extracellular SOD isoforms carry copper at the catalytic site, and copper is what performs the electron transfer. Copper status is part of what determines endogenous SOD activity.

Zinc occupies the structural site of Cu/Zn-SOD and holds the active-site geometry stable. It does not run the reaction itself but the enzyme folds and functions around it.

The mitochondrial isoform MnSOD carries manganese at its catalytic centre. Manganese supply feeds the isoform that sits closest to where superoxide is generated during normal respiration.

Ascorbate acts on radical species in the water phase that an enzyme specific to superoxide does not touch, and it regenerates oxidised tocopherol at the membrane surface. The two sit at different points of one network.

SOD works in aqueous compartments while alpha-tocopherol interrupts lipid peroxidation chains inside membranes. The two cover different phases of the same normal oxidative housekeeping.

Lipoic acid and its reduced form regenerate ascorbate and glutathione, which are the carriers that finish the job SOD starts. It is soluble in both water and lipid, so it bridges the two compartments.

NAC supplies cysteine, the rate-limiting amino acid for glutathione synthesis. More glutathione means more capacity to clear the peroxide that SOD activity produces.

Loosely bound ferrous iron reacts with hydrogen peroxide through Fenton chemistry and yields hydroxyl radicals. Raising superoxide dismutation without matching peroxide clearance in the presence of free iron shifts the chemistry rather than ending it, which is why catalase or glutathione capacity belongs alongside.

Ergothioneine is taken up by a dedicated transporter and concentrates in mitochondria, the compartment where MnSOD works. It buffers thiol oxidation in the same location rather than duplicating SOD activity.

Superoxide dismutase converts superoxide to hydrogen peroxide, and something else has to remove that peroxide. Glutathione peroxidase does it at the cost of two glutathione molecules, and glutathione reductase puts them back using an FAD cofactor built from riboflavin. Without adequate riboflavin the recycling step runs slower, so the downstream half of the pathway is riboflavin dependent.

Sulforaphane modifies cysteine residues on Keap1, releasing Nrf2 to enter the nucleus and switch on antioxidant response element genes. That is a route to more of the body's own dismutase rather than more supplemental enzyme. The two approaches, supplying the protein and inducing its expression, are different and are often described as if they were the same thing.

Broccoli sprout material supplies glucoraphanin, which myrosinase converts to sulforaphane either in the plant when it is chewed or by gut bacteria. The resulting sulforaphane induces the antioxidant response element genes that include the dismutase isoforms. Conversion efficiency varies with whether active myrosinase is present in the product.

Curcuminoids modify Keap1 thiols and increase antioxidant response element gene expression in cell and animal models, with superoxide dismutase among the genes reported. Curcumin's own oral absorption is low without a delivery aid, which limits how much of this reaches tissue. Gene expression is a marker, not a clinical outcome.

Pterostilbene, the dimethylated relative of resveratrol, activates the same antioxidant response element pathway in cell models and is more metabolically stable than resveratrol because two hydroxyls are methylated. The result would be more endogenous enzyme rather than more supplemental protein. Evidence here is preclinical.

Complex I and complex III leak electrons to oxygen, producing superoxide inside the mitochondrial matrix where manganese superoxide dismutase handles it. Ubiquinol carries electrons within that chain and also acts as a lipid-phase antioxidant in the inner membrane. The two operate at the same site on the same problem from different angles.

Hydrogen peroxide produced downstream of dismutation can be used by myeloperoxidase to make hypochlorous acid, a far more reactive species. Taurine traps hypochlorous acid as taurine chloramine, which is much less reactive. That is a distinct step from dismutation and downstream of it.

Melatonin scavenges reactive species directly and its oxidation products remain active as scavengers, a cascade described in cell-free and cell systems. It also concentrates in mitochondria, the compartment where most superoxide is generated. Direct scavenging is stoichiometric and slower than enzymatic dismutation, so the two are not interchangeable.

Singlet oxygen is a different reactive species from superoxide and needs a different handler; the extended conjugated chain of lycopene quenches it physically by absorbing the excess energy. Dismutase does not act on singlet oxygen at all. The pairing covers two separate reactive species.

Green tea catechins donate hydrogen atoms to radicals and, at cellular concentrations, activate antioxidant response element genes. At higher concentrations catechins can themselves generate hydrogen peroxide in culture media, which is a laboratory artefact worth knowing about when reading in vitro results. Both observations are mechanistic.

An orally administered enzyme has no special protection from digestion. Pepsin cleaves it at acidic gastric pH into peptides that have no dismutase activity, which is exactly why commercial oral forms use a protective coating such as a gliadin complex or an enteric shell. Adding supplemental pepsin works directly against that protection.

Lowering gastric pH increases both acid denaturation of the protein and the activity of pepsin, which is optimal in the acidic range. A supplement taken to acidify the stomach therefore reduces the chance an uncoated enzyme survives. Timing the two apart is the practical response.

Trypsin and chymotrypsin cleave peptide bonds in the small intestine, which is precisely where an enteric-coated enzyme releases its contents. Protein-based enzyme supplements face this second barrier after the stomach. It is the central reason oral enzyme delivery is difficult.

Digestive enzyme blends usually include proteases, which do not distinguish a dietary protein from a supplemental one. Taking a protein-based enzyme alongside them shortens its survival. Separating them by time is straightforward.

Xanthine oxidoreductase uses a molybdenum cofactor and, in its oxidase form, produces superoxide and hydrogen peroxide while oxidising hypoxanthine and xanthine. That places molybdenum on the production side of the same chemistry the dismutase handles. This is an upstream relationship, not a shared function.

Grape seed procyanidins act as hydrogen donors and also bind iron and copper, which reduces metal-catalysed conversion of hydrogen peroxide into the far more damaging hydroxyl radical. That addresses the step immediately after dismutation. Most of this evidence is in vitro.

Pine bark extract supplies procyanidins that quench radicals and bind free transition metals in solution. Free iron or copper turns hydrogen peroxide, the product of dismutation, into hydroxyl radicals, so metal binding matters at that step. The evidence base here is mostly laboratory work.

C-phycocyanin, the blue pigment protein of spirulina, scavenges radicals in cell-free systems, and animal studies report changes in tissue antioxidant enzyme activity after spirulina feeding. Enzyme activity in tissue is a marker. The pigment is itself a protein and subject to the same digestion question as any oral enzyme.

Because astaxanthin sits across the membrane rather than within the hydrophobic core, it can quench radicals at both the inner and outer membrane surfaces. Superoxide dismutase works in the aqueous compartments, cytosolic, mitochondrial and extracellular. Together they cover the lipid and aqueous phases, which is the standard argument for a mixed antioxidant formula.