What Is Sulfation in Peptides? Tyrosine Sulfation, Explained

Published October 2026 · Patriot Labs Research Team · ~20 min read

The short answer

Sulfation in peptides is the attachment of a sulfate group (SO₃⁻) to the hydroxyl of a tyrosine side chain, forming a tyrosine O-sulfate ester. An enzyme called tyrosylprotein sulfotransferase (TPST) transfers the sulfate from a donor molecule, PAPS, as a protein passes through the Golgi. It is the most common modification of secreted and cell-surface proteins at tyrosine, and it is found only on proteins that travel the secretory pathway.^[1][2]

What makes sulfation worth a guide of its own is a coincidence of chemistry: a sulfate group weighs almost exactly the same as a phosphate, and it lands on the same amino acid — tyrosine — that phosphorylation most famously decorates. On an ordinary mass spectrometer the two modifications are indistinguishable, which is part of why sulfation was overlooked for so long. But they are opposites in several ways that matter. A phosphate is added and removed on demand by kinases and phosphatases and acts as a fast, reversible switch inside the cell; a sulfate is installed once in the Golgi, has no known enzyme to remove it, and is carried out of the cell on secreted proteins as an effectively permanent mark.^[1][2][15]

The rest of this guide takes it in order — the bond, the residue, the enzyme and donor, the effect, the proteins it is studied on, the analytical signature, and the chemistry of making a sulfopeptide on purpose — and ends with what the topic does and does not tell a researcher about a research vial.

The sulfate group and the bond it forms

Sulfation attaches a sulfate — a sulfur atom surrounded by four oxygens — to a tyrosine by forming a covalent bond to the oxygen of the side-chain hydroxyl. The product is a tyrosine O-sulfate ester, more precisely an aryl sulfate ester, because the oxygen that carries the sulfate belongs to tyrosine’s aromatic phenol ring. The modified residue is called sulfotyrosine, often written sTyr or Tyr(SO₃H).^[1][3]

As with phosphorylation, the chemistry that follows is dominated by charge. A plain tyrosine hydroxyl is neutral. The sulfate that replaces its hydrogen carries a full negative charge across the whole physiological range: the sulfate ester is strongly acidic, so at the neutral pH of the extracellular space it sits essentially always in its ionised, singly negative form. In one step the cell has planted a fixed anion at a defined point on the protein surface. That is the structural fact behind everything sulfation does — it converts an unremarkable aromatic residue into a hard negative charge that other molecules can grip.^[1][3]

There is one more property of the bond that shapes the entire practical story of sulfation: the aryl sulfate ester is acid-labile. Expose a sulfotyrosine to acid and the sulfate hydrolyses off, regenerating the plain tyrosine. This fragility is why the modification is so easily lost during analysis and so awkward to build by synthesis, both of which are covered below. It is a sharp contrast with the phosphotyrosine ester, which is far more robust.^[3][13]

Which amino acids get sulfated

Protein sulfation is, for practical purposes, a tyrosine story. In peptides and proteins the sulfate lands overwhelmingly on tyrosine, through the oxygen of its phenol hydroxyl, to give sulfotyrosine. Minor O-sulfation of serine and threonine has been reported, but it is not a meaningful feature of protein sulfation, and when a biochemist says a protein is “sulfated” they almost always mean tyrosine.^[1][4]

It is worth drawing one boundary clearly, because it is a common point of confusion. The sulfate groups on carbohydrates — the dense sulfation of heparin, heparan sulfate and the other glycosaminoglycans — are a different modification entirely. Those sulfates sit on sugar rings, are installed by a separate family of carbohydrate sulfotransferases, and have nothing to do with the tyrosine sulfation discussed here except the shared chemical label “sulfate.” This guide is about sulfation of the peptide: the sulfate on an amino acid side chain, not on an attached glycan.^[4]

The residue itself is an ordinary amino acid; sulfation is a cap added to tyrosine’s side chain, in much the same way that phosphorylation caps a serine, threonine or tyrosine hydroxyl. The difference is in what gets attached and, as the next section shows, in how and where the cell attaches it.

TPST and PAPS: how the sulfate is installed

Sulfation is run by a single, small enzyme family and a single sulfate donor. Tyrosylprotein sulfotransferase (TPST) transfers a sulfate from the donor PAPS onto a tyrosine. Humans have two isoforms, TPST1 and TPST2, of 370 and 377 amino acids; they share about 63% sequence identity overall, rising to roughly 77% across the catalytic domain. Both are integral membrane proteins of the trans-Golgi network, anchored with their active site facing into the Golgi lumen — which is exactly why only proteins routed through the secretory pathway can be sulfated.^[1][2][6]

The donor, PAPS (3′-phosphoadenosine-5′-phosphosulfate), is the cell’s universal “activated sulfate.” It is built from inorganic sulfate in two steps: ATP sulfurylase joins sulfate to ATP to make adenosine-5′-phosphosulfate (APS), and APS kinase then phosphorylates it to PAPS. TPST grabs PAPS and the target tyrosine, lines up the sulfate with the phenol oxygen, and transfers it, leaving behind PAP (3′,5′-ADP). Every sulfotransferase in the cell, whether it modifies a protein, a sugar or a small molecule, draws on this same PAPS pool.^[1][2]

Unlike phosphorylation, there is no opposing enzyme. The cell has a large toolkit of phosphatases that strip phosphate off proteins, but no protein tyrosine sulfatase is known to remove a sulfate from a tyrosine in the same regulatory way. Once TPST installs the sulfate in the Golgi, it stays; when the protein is eventually degraded, free tyrosine O-sulfate is released and excreted largely intact in the urine. For the researcher this is the headline difference from phosphorylation: sulfation is not a switch that is flipped back and forth but a permanent finishing step applied on the way out of the cell.^[2][15]

Which tyrosines get chosen is governed less by a tidy consensus sequence than by context. TPST favours tyrosines sitting in acidic neighbourhoods — stretches rich in glutamate and aspartate — and exposed on turns or disordered regions rather than buried in folded structure. There is no single strict motif, which is one reason sulfation sites are predicted rather than read off a simple rule; the Sulfinator tool was built specifically to estimate them from sequence.^[1][10]

What a sulfate actually changes

A sulfate changes a protein in essentially one way, and it is the same mechanism in every case: it plants a hard negative charge on an exposed surface, and that charge becomes part of how the protein touches its partners. Sulfotyrosine almost always sits in a region where one protein binds another, and the sulfate tunes the strength and specificity of that contact.^[2][3]

Because the modification lives on the outside of cells, on secreted and cell-surface proteins, its job is extracellular recognition rather than internal signalling. Where a phosphate usually toggles an intracellular enzyme on or off, a sulfate more often acts as a recognition handle: a negatively charged feature that a receptor, a ligand or an adhesion partner reads to decide how tightly to bind. Removing the sulfate, or mutating the tyrosine so it cannot be sulfated, typically weakens that interaction without destroying the protein — the fingerprint of a modification that fine-tunes binding rather than builds structure.^[3]

That single mechanism — a negative charge at a binding interface — is enough to matter across a surprising range of biology: blood clotting, the rolling of white blood cells along vessel walls, the docking of hormones onto their receptors, and the way some viruses grab a cell-surface protein. The examples below are all variations on it.

Sulfated proteins in the research literature

Sulfation stayed obscure partly because its best examples are scattered across unrelated fields. Pulled together, they make the pattern obvious: in each case a sulfotyrosine sits at a protein–protein interface and strengthens the grip.

PSGL-1 and leukocyte rolling. P-selectin glycoprotein ligand-1 carries a cluster of sulfotyrosines near its N-terminus, and a 1995 study showed that this sulfated segment is critical for binding P-selectin — the interaction that lets white blood cells tether and roll along a blood-vessel wall before leaving the circulation. Strip the sulfate and the binding falls away.^[8]

Coagulation factor VIII. Sulfation of a single tyrosine, Tyr1680, in blood coagulation factor VIII was shown in 1991 to be essential for the protein’s interaction with von Willebrand factor, the carrier that stabilises factor VIII in circulation. A one-atom-scale edit on one residue governs a clinically important binding event.^[9]

Hirudin and the gastrointestinal hormones. Hirudin, the anticoagulant protein from the medicinal leech, carries a sulfotyrosine (at position 63) that strengthens its already tight grip on thrombin. The peptide hormones gastrin and cholecystokinin (CCK) each carry a sulfotyrosine as well, and in CCK that sulfate is part of what the classic CCK receptor recognises — a case where the modification is written into the definition of the active molecule.^[1][3]

Chemokine receptors and CCR5. Many chemokine receptors carry sulfotyrosines in their extracellular N-terminal tails, where their chemokine ligands dock. The most studied case is CCR5: a 1999 study found that sulfation of tyrosines at the amino terminus of CCR5 takes part in how the HIV-1 envelope glycoprotein gp120 engages the receptor, tying a humble sulfate group to a central question in virology. It remains one of the clearest demonstrations that a sulfotyrosine can be decisive at a binding interface.^[7]

Prediction tools suggest these named cases are the visible tip of a much larger set: estimates put the fraction of sulfatable tyrosines in the secreted and membrane proteome at around 1%, with a few hundred sulfated proteins experimentally reported and sequence-based tools predicting several thousand candidates.^[1][10]

The +80-dalton signature and the phosphate look-alike

Sulfation adds a nominal 80 daltons of mass — the elements of SO₃ — which is the single most important and most inconvenient fact about detecting it, because phosphorylation adds the same nominal 80. On a low-resolution instrument the two are simply indistinguishable, and for years sulfation was mistaken for, or masked by, phosphorylation for exactly this reason.^[1]

The escape is exact mass. The monoisotopic increase for sulfation is about 79.9568 daltons, while phosphorylation adds about 79.9663 daltons — a gap of roughly 9.5 millidaltons. A high-resolution analyser such as an FT-ICR or Orbitrap instrument can resolve that difference and assign the modification to sulfate rather than phosphate with confidence. Without that resolving power, the two cannot be separated by mass alone.^[1][12]

Even with the right instrument, sulfotyrosine fights back. The O-sulfate ester is fragile, and in the positive-ion mode normally used for peptides it is often lost completely during ionisation and fragmentation — the sulfate simply falls off, leaving a signal that looks like the unmodified peptide and produces a false negative. Analysts work around this by switching to negative-ion mode, where the sulfate survives and reports characteristic fragments, and by using gentler fragmentation such as electron-capture or electron-transfer dissociation (ECD/ETD) that can pin the sulfate to a specific residue without knocking it off.^[12]

Other tools fill out the picture. A monoclonal antibody raised against sulfotyrosine (PSG2) lets sulfated proteins be detected and enriched, and the historical reference method — metabolic labelling with radioactive ³⁵S sulfate — remains sensitive if cumbersome.^[11] For a synthetic sulfopeptide the question is narrower — is the sulfate present, on the right tyrosine, and how pure is the product — and the answer comes from the same analytical pairing used for any peptide: HPLC for purity and mass spectrometry for identity, the methods an independent US laboratory uses to document a lot on a certificate of analysis.

How sulfopeptides are made in the lab

Sulfotyrosine peptides are made deliberately for research, and the whole challenge is the acid-lability of the O-sulfate ester. Ordinary solid-phase peptide synthesis ends with a strongly acidic step — trifluoroacetic acid to cleave the peptide from the resin and strip the side-chain protecting groups — and a bare sulfotyrosine does not survive it. Two strategies get a sulfate onto the finished peptide anyway, and they differ in when the sulfate goes on.^[13]

The building-block approach couples a pre-made, protected sulfotyrosine into the chain like any other residue. The modern form uses an Fmoc-protected sulfotyrosine whose sulfate is itself capped with an acid-stable protecting group — the neopentyl ester, giving a reagent written Fmoc-Tyr(SO₃nP)-OH — so the sulfate rides through the acidic cleavage intact and is unmasked in a controlled final step. This building-block route is clean and predictable for a peptide with one or two defined sulfation sites.^[13]

The global, or post-assembly, approach builds the whole peptide first with the target tyrosine left free, then sulfates it directly using a sulfur trioxide complex — typically SO₃·pyridine or a related SO₃ amine adduct — and finally removes the remaining protecting groups under carefully mild conditions so the fresh sulfate is not lost. This was the route used in the classic total syntheses of sulfated peptide hormones such as big gastrin-II and the cholecystokinin fragment CCK-39.^[14]

Whichever route is chosen, the finished sulfopeptide is characterised the same way any peptide is — purity by HPLC, identity and the presence of the sulfate by mass spectrometry, read in a mode that keeps the fragile sulfate intact. The broader toolkit of Fmoc synthesis, the resins, coupling reagents and cleavage cocktails, is the same one used for every modified peptide and is covered in the manufacturing guide.

Sulfation next to the other modifications

Sulfation is best understood by its contrast with phosphorylation, the modification it imitates on the scale and mimics on the residue. Both put about 80 daltons onto a tyrosine; everything else about them diverges. Phosphorylation is reversible, intracellular and regulatory — a switch; sulfation is permanent, extracellular and architectural — a finishing touch that sets how a secreted protein binds. That the two are so easily confused by mass is a quirk of chemistry, not a sign of related function.^[1][2]

Set against the wider family, sulfation’s niche is narrow and specific. Acetylation adds a small neutral group that chiefly removes a positive charge; C-terminal amidation is a permanent finishing step that neutralises a terminal charge; glycosylation hangs whole carbohydrate trees off the protein and can itself carry sulfates on its sugars. Sulfation does something none of these do: it installs a single, fixed, strong negative charge on one tyrosine on the outside of a cell, precisely where one protein meets another. For more on how such edits extend or alter a peptide, see the overview of half-life extension.

A short history: from fibrinogen to sulfoproteomics

Tyrosine sulfation was discovered in 1954, when F. R. Bettelheim identified tyrosine-O-sulfate in a peptide released from fibrinogen — the first time a sulfate had been pinned to a specific amino acid in a protein.^[5] Like early phosphorylation, it looked at first like a chemical curiosity rather than a widespread or regulated modification, and for a quarter of a century it attracted little attention.

The modern understanding began when the responsible enzyme was found. Tyrosylprotein sulfotransferase activity was first demonstrated in cell lysates in the early 1980s, establishing that sulfation was an enzyme-catalysed, PAPS-dependent event in the Golgi rather than an accident. The field’s turning point came in 1998, when Ouyang, Lane and Moore purified and cloned TPST, revealing the enzyme family (soon shown to have two human isoforms) behind a modification that had been known for forty years.^[6]

From there, appreciation of its scope grew. The named examples — PSGL-1, factor VIII, the chemokine receptors — accumulated through the 1990s and 2000s, and sequence-prediction tools such as the Sulfinator put rough numbers on how common sulfation might be across the proteome.^[10] The remaining obstacle has always been analytical: because sulfation hides behind phosphorylation by mass and is lost under the usual conditions, building a true “sulfoproteomics” has lagged behind phosphoproteomics, and the development of synthetic sulfopeptide standards and gentler mass-spectrometry methods has been aimed squarely at closing that gap.^[4][13]

What this guide does not establish

This is a chemistry and biology explainer, and its scope is deliberately narrow. It describes what tyrosine sulfation is and how it is studied; it does not describe any use of a peptide in a person or animal, and nothing here is medical, veterinary or dosing advice. The proteins named above — PSGL-1, factor VIII, hirudin, gastrin, cholecystokinin, CCR5 — are discussed as subjects of published biochemistry, in their natural biological settings, not as products of any kind.

Two further cautions. First, whether a particular catalogue peptide carries a sulfotyrosine is a property of its defined sequence: a sulfopeptide is a distinct molecule with the sulfate written into its specification, and only its own certificate of analysis speaks to what a given lot actually contains — a point sharpened by the fact that the sulfate is easily lost and must be confirmed with care. Second, the statistics quoted here (the ∼1% figure, the few hundred reported proteins, the predicted thousands) are population-level estimates from the cited studies and tools; they describe the sulfoproteome at large, not any single molecule. For what a certificate of analysis can and cannot prove about an individual vial, see Understanding Peptide COA Testing.

Frequently asked questions

What is sulfation in peptides?

Sulfation in peptides is the attachment of a sulfate group (SO3) to the hydroxyl of a tyrosine side chain, forming a tyrosine O-sulfate ester. An enzyme called tyrosylprotein sulfotransferase (TPST) transfers the sulfate from a donor molecule called PAPS as a protein passes through the Golgi. It is the most common modification of secreted and membrane proteins at tyrosine, and it is found only on proteins that travel the secretory pathway.

What is the difference between sulfation and phosphorylation?

Both add a group of almost exactly 80 daltons to a tyrosine, so on a low-resolution instrument they look identical, but they are different chemistries doing different jobs. Phosphorylation adds a phosphate and is reversible: a kinase puts it on and a phosphatase takes it off, which makes it a fast signalling switch inside the cell. Sulfation adds a sulfate, is installed only in the Golgi by TPST, and has no known enzyme that removes it, so it is treated as effectively permanent. Sulfation occurs on secreted and extracellular proteins; regulatory phosphorylation occurs largely on intracellular ones. By exact mass, sulfation adds 79.9568 daltons and phosphorylation 79.9663 daltons, a difference of about 9.5 millidaltons that a high-resolution mass spectrometer can resolve.

What amino acid is sulfated in peptides?

In peptides and proteins, sulfation lands almost entirely on tyrosine, through the oxygen of its phenol hydroxyl, giving sulfotyrosine. This is distinct from the sulfation of carbohydrates, such as the sulfate groups on heparan sulfate and other glycosaminoglycans, which sit on sugars rather than on the peptide backbone. Minor O-sulfation of serine and threonine has been described but is not a significant feature of protein sulfation.

How much mass does sulfation add to a peptide?

One sulfate group adds a nominal 80 daltons, from the addition of SO3. The exact monoisotopic increase is about 79.9568 daltons. That nominal 80 is the same as phosphorylation, which is why the two cannot be told apart by mass alone on a low-resolution instrument; only a high-resolution measurement, which resolves the roughly 9.5-millidalton gap between the two, or a method that reads the chemistry directly, distinguishes them.

Is tyrosine sulfation reversible?

No known enzyme reverses tyrosine sulfation, so unlike phosphorylation it is treated as an effectively permanent modification rather than an on/off switch. Tyrosine O-sulfate released when a sulfated protein is broken down is excreted largely intact. This is one of the clearest differences between sulfation and phosphorylation: both add about 80 daltons to a tyrosine, but only phosphorylation is routinely added and removed.

Can synthetic peptides be sulfated?

Yes. Sulfotyrosine peptides are made on purpose by solid-phase peptide synthesis, in two main ways. The building-block approach couples a ready-made protected sulfotyrosine, such as an Fmoc-protected, neopentyl-stabilised sulfotyrosine, into the chain at the right position. The global, or post-assembly, approach builds the peptide first and then sulfates the free tyrosine with a sulfur trioxide complex such as SO3-pyridine. The central difficulty is that the tyrosine O-sulfate ester is acid-labile and tends to be lost under the strongly acidic conditions used to cleave and deprotect a peptide, so the chemistry is designed around protecting it.

Why is sulfotyrosine hard to detect by mass spectrometry?

The tyrosine O-sulfate ester is fragile. In positive-ion mode, the usual setting for peptide analysis, the sulfate is often lost completely during ionisation and fragmentation, leaving a signal that looks like the unmodified peptide and causing false negatives. Analysts work around this by using negative-ion mode, gentler fragmentation methods such as electron-capture or electron-transfer dissociation, and high-resolution instruments that separate the sulfate's exact mass from that of a phosphate.

What proteins are tyrosine-sulfated?

Tyrosine sulfation is found on many secreted and cell-surface proteins. Well-studied examples from the research literature include the leukocyte adhesion protein PSGL-1, blood coagulation factor VIII, the leech anticoagulant protein hirudin, the peptide hormones gastrin and cholecystokinin, and the N-terminal regions of several chemokine receptors, including CCR5, where sulfotyrosines were shown to take part in how HIV-1 engages the receptor. Prediction tools estimate that a low single-digit percentage of all tyrosines in the secreted and membrane proteome may be sulfated.

References

1. Yang, Y.-S., Wang, C.-C., Chen, B.-H., Hou, Y.-H., Hung, K.-S., & Mao, Y.-C. (2015). Tyrosine Sulfation as a Protein Post-Translational Modification. Molecules, 20(2), 2138–2164. doi:10.3390/molecules20022138
2. Moore, K. L. (2003). The biology and enzymology of protein tyrosine O-sulfation. Journal of Biological Chemistry, 278(27), 24243–24246. doi:10.1074/jbc.R300008200
3. Kehoe, J. W., & Bertozzi, C. R. (2000). Tyrosine sulfation: a modulator of extracellular protein–protein interactions. Chemistry & Biology, 7(3), R57–R61. doi:10.1016/S1074-5521(00)00093-4
4. Stone, M. J., Chuang, S., Hou, X., Shoham, M., & Zhu, J. Z. (2009). Tyrosine sulfation: an increasingly recognised post-translational modification of secreted proteins. New Biotechnology, 25(5), 299–317. doi:10.1016/j.nbt.2009.03.011
5. Bettelheim, F. R. (1954). Tyrosine-O-sulfate in a peptide from fibrinogen. Journal of the American Chemical Society, 76(10), 2838–2839. doi:10.1021/ja01639a073
6. Ouyang, Y.-B., Lane, W. S., & Moore, K. L. (1998). Tyrosylprotein sulfotransferase: Purification and molecular cloning of an enzyme that catalyzes tyrosine O-sulfation, a common posttranslational modification of eukaryotic proteins. Proceedings of the National Academy of Sciences USA, 95(6), 2896–2901. doi:10.1073/pnas.95.6.2896
7. Farzan, M., Mirzabekov, T., Kolchinsky, P., Wyatt, R., Cayabyab, M., Gerard, N. P., Gerard, C., Sodroski, J., & Choe, H. (1999). Tyrosine sulfation of the amino terminus of CCR5 facilitates HIV-1 entry. Cell, 96(5), 667–676. doi:10.1016/S0092-8674(00)80577-2
8. Sako, D., Comess, K. M., Barone, K. M., Camphausen, R. T., Cumming, D. A., & Shaw, G. D. (1995). A sulfated peptide segment at the amino terminus of PSGL-1 is critical for P-selectin binding. Cell, 83(2), 323–331. doi:10.1016/0092-8674(95)90173-6
9. Leyte, A., van Schijndel, H. B., Niehrs, C., Huttner, W. B., Verbeet, M. P., Mertens, K., & van Mourik, J. A. (1991). Sulfation of Tyr1680 of human blood coagulation factor VIII is essential for the interaction of factor VIII with von Willebrand factor. Journal of Biological Chemistry, 266(2), 740–746. doi:10.1016/S0021-9258(17)35234-1
10. Monigatti, F., Gasteiger, E., Bairoch, A., & Jung, E. (2002). The Sulfinator: predicting tyrosine sulfation sites in protein sequences. Bioinformatics, 18(5), 769–770. doi:10.1093/bioinformatics/18.5.769
11. Hoffhines, A. J., Damoc, E., Bridges, K. G., Leary, J. A., & Moore, K. L. (2006). Detection and purification of tyrosine-sulfated proteins using a novel anti-sulfotyrosine monoclonal antibody. Journal of Biological Chemistry, 281(49), 37877–37887. doi:10.1074/jbc.M609398200
12. Edelson-Averbukh, M., Shevchenko, A., Pipkorn, R., & Lehmann, W. D. (2011). Discrimination between peptide O-sulfo- and O-phosphotyrosine residues by negative ion mode electrospray tandem mass spectrometry. Journal of the American Society for Mass Spectrometry, 22(12), 2256–2268. doi:10.1007/s13361-011-0248-z
13. Seibert, C., & Sakmar, T. P. (2008). Toward a framework for sulfoproteomics: Synthesis and characterization of sulfotyrosine-containing peptides. Biopolymers (Peptide Science), 90(3), 459–477. doi:10.1002/bip.20821
14. Kitagawa, K., Aida, C., Fujiwara, H., Yagami, T., Futaki, S., Kogire, M., Ida, J., & Inoue, K. (2001). Facile solid-phase synthesis of sulfated tyrosine-containing peptides: total synthesis of human big gastrin-II and cholecystokinin (CCK)-39. The Journal of Organic Chemistry, 66(1), 1–10. doi:10.1021/jo000895y
15. Tyrosine sulfation. Wikipedia. https://en.wikipedia.org/wiki/Tyrosine_sulfation

For more on the chemistry this guide touches, see What Is Phosphorylation? for the +80-dalton modification sulfation is most often confused with, What Is Glycosylation? for the sugar-based modification that can itself carry sulfates, What Is Acetylation? for another small side-chain and terminal edit, What Is Solid-Phase Peptide Synthesis? for how a sulfopeptide is actually built, and Understanding Peptide COA Testing for how HPLC and mass spectrometry document what is in a vial.

All Patriot Labs products are sold strictly for in-vitro research and laboratory use only. Not for human or veterinary consumption. This guide is educational and explains tyrosine sulfation as a topic in peptide and protein chemistry; it is not medical advice, does not describe how to use any product, and makes no therapeutic claim.