You are using an unsupported browser. Please upgrade your browser to a newer version to get the best experience on Human Metabolome Database.
Record Information
Version4.0
StatusDetected and Quantified
Creation Date2006-02-22 11:10:26 UTC
Update Date2019-03-14 18:02:07 UTC
HMDB IDHMDB0001860
Secondary Accession Numbers
  • HMDB01860
Metabolite Identification
Common NameParaxanthine
Description1,7-dimethylxanthine (paraxanthine) is the preferential path of caffeine metabolism in humans. Paraxanthine is a dimethylxanthine compound structurally related to caffeine. Like caffeine, paraxanthine is a psychoactive central nervous system (CNS) stimulant. It possesses a potency roughly equal to that of caffeine and is likely involved in the mediation of the effects of caffeine itself.
Structure
Data?1547234175
Synonyms
ValueSource
3,7-Dihydro-1,7-dimethyl-1H-purine-2,6-dioneChEBI
p-XanthineChEBI
1,7-Dimethyl-xanthineHMDB
1,7-DimethylxanthineHMDB
Chemical FormulaC7H8N4O2
Average Molecular Weight180.164
Monoisotopic Molecular Weight180.06472552
IUPAC Name1,7-dimethyl-2,3,6,7-tetrahydro-1H-purine-2,6-dione
Traditional Nameparaxanthine
CAS Registry Number611-59-6
SMILES
CN1C=NC2=C1C(=O)N(C)C(=O)N2
InChI Identifier
InChI=1S/C7H8N4O2/c1-10-3-8-5-4(10)6(12)11(2)7(13)9-5/h3H,1-2H3,(H,9,13)
InChI KeyQUNWUDVFRNGTCO-UHFFFAOYSA-N
Chemical Taxonomy
Description belongs to the class of organic compounds known as xanthines. These are purine derivatives with a ketone group conjugated at carbons 2 and 6 of the purine moiety.
KingdomOrganic compounds
Super ClassOrganoheterocyclic compounds
ClassImidazopyrimidines
Sub ClassPurines and purine derivatives
Direct ParentXanthines
Alternative Parents
Substituents
  • Xanthine
  • 6-oxopurine
  • Purinone
  • Alkaloid or derivatives
  • Pyrimidone
  • Hydroxypyrimidine
  • N-substituted imidazole
  • Pyrimidine
  • Imidazole
  • Azole
  • Heteroaromatic compound
  • Lactam
  • Azacycle
  • Hydrocarbon derivative
  • Organic oxide
  • Organopnictogen compound
  • Organic oxygen compound
  • Organooxygen compound
  • Organonitrogen compound
  • Organic nitrogen compound
  • Aromatic heteropolycyclic compound
Molecular FrameworkAromatic heteropolycyclic compounds
External Descriptors
Ontology
Disposition

Source:

Biological location:

Process

Naturally occurring process:

Role

Biological role:

Physical Properties
StateSolid
Experimental Properties
PropertyValueReference
Melting Point351 - 352 °CNot Available
Boiling PointNot AvailableNot Available
Water SolubilityNot AvailableNot Available
LogPNot AvailableNot Available
Predicted Properties
PropertyValueSource
Water Solubility9.13 g/LALOGPS
logP-0.63ALOGPS
logP0.24ChemAxon
logS-1.3ALOGPS
pKa (Strongest Acidic)10.76ChemAxon
pKa (Strongest Basic)-0.87ChemAxon
Physiological Charge0ChemAxon
Hydrogen Acceptor Count3ChemAxon
Hydrogen Donor Count1ChemAxon
Polar Surface Area67.23 ŲChemAxon
Rotatable Bond Count0ChemAxon
Refractivity46.72 m³·mol⁻¹ChemAxon
Polarizability16.87 ųChemAxon
Number of Rings2ChemAxon
Bioavailability1ChemAxon
Rule of FiveYesChemAxon
Ghose FilterYesChemAxon
Veber's RuleYesChemAxon
MDDR-like RuleYesChemAxon
Spectra
Spectrum TypeDescriptionSplash KeyView
GC-MSGC-MS Spectrum - GC-EI-TOF (Pegasus III TOF-MS system, Leco; GC 6890, Agilent Technologies) (Non-derivatized)splash10-000i-2980000000-6ee5dc3100885f205536JSpectraViewer | MoNA
GC-MSGC-MS Spectrum - GC-EI-TOF (Non-derivatized)splash10-000i-2980000000-6ee5dc3100885f205536JSpectraViewer | MoNA
Predicted GC-MSPredicted GC-MS Spectrum - GC-MS (Non-derivatized) - 70eV, Positivesplash10-0uka-3900000000-d979badf45de391835d4JSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - Quattro_QQQ 10V, Positive (Annotated)splash10-001i-0900000000-2d1aa5f80618f452686cJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - Quattro_QQQ 25V, Positive (Annotated)splash10-00di-0900000000-3326bcbee23b63dcc230JSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - Quattro_QQQ 40V, Positive (Annotated)splash10-014l-9000000000-9824aef9dc2f13c24bccJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - LC-ESI-QTOF (UPLC Q-Tof Premier, Waters) , Positivesplash10-00e9-1900000000-9d0dde13bb1ce13e2644JSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - LC-ESI-QTOF (UPLC Q-Tof Premier, Waters) , Negativesplash10-00fr-0900000000-1aa733a1b7e41b994d8dJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - LC-ESI-qTof , Positivesplash10-00di-1900000000-190ff3302e9f5a37a72fJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - LC-ESI-QTOF , negativesplash10-00fr-0900000000-1aa733a1b7e41b994d8dJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - Linear Ion Trap , negativesplash10-0229-0900000000-729a2bed81ba15260ffaJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - Linear Ion Trap , negativesplash10-0229-0900000000-18d0a9c63a1dfb683c9bJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - , negativesplash10-004i-0900000000-c52421f0ba1f46241853JSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - LC-ESI-IT , positivesplash10-00di-0900000000-0bd6ed3d764e5a9b374eJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - LC-ESI-QTOF , positivesplash10-00e9-1900000000-9d0dde13bb1ce13e2644JSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - Linear Ion Trap , positivesplash10-0w29-0940000000-127f99d8e7324e01eb66JSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - Linear Ion Trap , positivesplash10-0ik9-0930000000-fe234438cbe3be0b30f6JSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - , positivesplash10-00di-1900000000-190ff3302e9f5a37a72fJSpectraViewer | MoNA
LC-MS/MSLC-MS/MS Spectrum - , positivesplash10-001i-0900000000-d6040ea84fe19d8c5cc6JSpectraViewer | MoNA
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 10V, Positivesplash10-001i-0900000000-5e7c398698bb5c16617dJSpectraViewer | MoNA
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 20V, Positivesplash10-00di-1900000000-522eaddc21ef92e70e62JSpectraViewer | MoNA
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 40V, Positivesplash10-0005-9200000000-d10a1141c0e21f56ec00JSpectraViewer | MoNA
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 10V, Negativesplash10-004i-1900000000-bc2d3cb520a4fcb81529JSpectraViewer | MoNA
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 20V, Negativesplash10-004i-2900000000-e2e2992ce9b1265af790JSpectraViewer | MoNA
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 40V, Negativesplash10-05am-9300000000-e1aefedceb8692ffe91fJSpectraViewer | MoNA
1D NMR1H NMR SpectrumNot AvailableJSpectraViewer
2D NMR[1H,13C] 2D NMR SpectrumNot AvailableJSpectraViewer
Biological Properties
Cellular Locations
  • Cytoplasm (predicted from logP)
Biospecimen Locations
  • Blood
  • Cerebrospinal Fluid (CSF)
  • Feces
  • Saliva
  • Urine
Tissue Locations
  • Kidney
  • Liver
  • Prostate
Pathways
Normal Concentrations
BiospecimenStatusValueAgeSexConditionReferenceDetails
BloodDetected but not Quantified Adult (>18 years old)Both
Normal
details
BloodDetected but not Quantified Adult (>18 years old)Both
Normal
details
BloodDetected but not Quantified Adult (>18 years old)Both
Normal
details
BloodDetected and Quantified10.0 (0.30-28.0) uMAdult (>18 years old)BothNormal details
FecesDetected but not Quantified Adult (>18 years old)Both
Normal
details
FecesDetected but not Quantified Adult (>18 years old)Both
Normal
details
FecesDetected but not Quantified Adult (>18 years old)Both
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Not SpecifiedNormal details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
SalivaDetected but not Quantified Adult (>18 years old)Male
Normal
details
UrineDetected and Quantified3.44 +/- 2 umol/mmol creatinineChildren (1 - 13 years old)Not Specified
Normal
    • Mordechai, Hien, ...
details
UrineDetected and Quantified2.5 (3.2-4.0) umol/mmol creatinineAdult (>18 years old)BothNormal details
Abnormal Concentrations
BiospecimenStatusValueAgeSexConditionReferenceDetails
BloodDetected but not Quantified Adult (>18 years old)Both
Colorectal adenoma
details
Cerebrospinal Fluid (CSF)Detected and Quantified1.780 +/- 0.641 uMAdult (>18 years old)Not SpecifiedFavorable outcome from traumatic brain injury details
Cerebrospinal Fluid (CSF)Detected and Quantified0.833 +/- 1.163 uMAdult (>18 years old)MaleTraumatic Brain Injury (TBI) details
Cerebrospinal Fluid (CSF)Detected and Quantified1.200 +/- 1.373 uMAdult (>18 years old)FemaleTraumatic Brain Injury (TBI) details
Cerebrospinal Fluid (CSF)Detected and Quantified0.703 +/- 0.230 uMAdult (>18 years old)Not Specified
Traumatic brain injury
details
Cerebrospinal Fluid (CSF)Detected and Quantified0.931 +/- 0.221 uMAdult (>18 years old)Not SpecifiedTraumatic brain injury (TBI) details
FecesDetected but not Quantified Adult (>18 years old)Both
Colorectal cancer
details
FecesDetected but not Quantified Adult (>18 years old)BothColorectal Cancer details
UrineDetected and Quantified18.676 +/- 26.196 umol/mmol creatinineChildren (1 - 13 years old)Not Specified
Eosinophilic esophagitis
    • Mordechai, Hien, ...
details
UrineDetected but not Quantified Adult (>18 years old)Both
Colorectal adenoma
details
UrineDetected and Quantified3.6 (1.8-5.4) umol/mmol creatinineAdult (>18 years old)Both
Asthma
details
Associated Disorders and Diseases
Disease References
Traumatic brain injury
  1. Sachse KT, Jackson EK, Wisniewski SR, Gillespie DG, Puccio AM, Clark RS, Dixon CE, Kochanek PM: Increases in cerebrospinal fluid caffeine concentration are associated with favorable outcome after severe traumatic brain injury in humans. J Cereb Blood Flow Metab. 2008 Feb;28(2):395-401. Epub 2007 Aug 8. [PubMed:17684518 ]
Head injury
  1. Sachse KT, Jackson EK, Wisniewski SR, Gillespie DG, Puccio AM, Clark RS, Dixon CE, Kochanek PM: Increases in cerebrospinal fluid caffeine concentration are associated with favorable outcome after severe traumatic brain injury in humans. J Cereb Blood Flow Metab. 2008 Feb;28(2):395-401. Epub 2007 Aug 8. [PubMed:17684518 ]
Colorectal cancer
  1. Brown DG, Rao S, Weir TL, O'Malia J, Bazan M, Brown RJ, Ryan EP: Metabolomics and metabolic pathway networks from human colorectal cancers, adjacent mucosa, and stool. Cancer Metab. 2016 Jun 6;4:11. doi: 10.1186/s40170-016-0151-y. eCollection 2016. [PubMed:27275383 ]
  2. Goedert JJ, Sampson JN, Moore SC, Xiao Q, Xiong X, Hayes RB, Ahn J, Shi J, Sinha R: Fecal metabolomics: assay performance and association with colorectal cancer. Carcinogenesis. 2014 Sep;35(9):2089-96. doi: 10.1093/carcin/bgu131. Epub 2014 Jul 18. [PubMed:25037050 ]
Asthma
  1. Zydron M, Baranowski J, Baranowska I: Separation, pre-concentration, and HPLC analysis of methylxanthines in urine samples. J Sep Sci. 2004 Oct;27(14):1166-72. [PubMed:15537072 ]
Eosinophilic esophagitis
  1. (). Mordechai, Hien, and David S. Wishart. .
Associated OMIM IDs
DrugBank IDNot Available
Phenol Explorer Compound IDNot Available
FoodDB IDFDB022714
KNApSAcK IDC00039930
Chemspider ID4525
KEGG Compound IDC13747
BioCyc ID1-7-DIMETHYLXANTHINE
BiGG IDNot Available
Wikipedia LinkParaxanthine
METLIN ID1457
PubChem Compound4687
PDB IDNot Available
ChEBI ID25858
References
Synthesis ReferenceMueller, Christa E.; Deters, Dirk; Dominik, Andreas; Pawlowski, Maciej. Synthesis of paraxanthine and isoparaxanthine analogs (1,7- and 1,9-substituted xanthine derivatives). Synthesis (1998), (10), 1428-1436.
Material Safety Data Sheet (MSDS)Download (PDF)
General References
  1. Sreekumar A, Poisson LM, Rajendiran TM, Khan AP, Cao Q, Yu J, Laxman B, Mehra R, Lonigro RJ, Li Y, Nyati MK, Ahsan A, Kalyana-Sundaram S, Han B, Cao X, Byun J, Omenn GS, Ghosh D, Pennathur S, Alexander DC, Berger A, Shuster JR, Wei JT, Varambally S, Beecher C, Chinnaiyan AM: Metabolomic profiles delineate potential role for sarcosine in prostate cancer progression. Nature. 2009 Feb 12;457(7231):910-4. doi: 10.1038/nature07762. [PubMed:19212411 ]
  2. Christensen M, Andersson K, Dalen P, Mirghani RA, Muirhead GJ, Nordmark A, Tybring G, Wahlberg A, Yasar U, Bertilsson L: The Karolinska cocktail for phenotyping of five human cytochrome P450 enzymes. Clin Pharmacol Ther. 2003 Jun;73(6):517-28. [PubMed:12811361 ]
  3. Fuhr U, Rost KL: Simple and reliable CYP1A2 phenotyping by the paraxanthine/caffeine ratio in plasma and in saliva. Pharmacogenetics. 1994 Jun;4(3):109-16. [PubMed:7920690 ]
  4. Tanaka E: Simultaneous determination of caffeine and its primary demethylated metabolites in human plasma by high-performance liquid chromatography. J Chromatogr. 1992 Mar 27;575(2):311-4. [PubMed:1629311 ]
  5. Horrigan LA, Kelly JP, Connor TJ: Immunomodulatory effects of caffeine: friend or foe? Pharmacol Ther. 2006 Sep;111(3):877-92. Epub 2006 Mar 15. [PubMed:16540173 ]
  6. Holstege A, Kurz M, Weinbeck M, Gerok W: Excretion of caffeine and its primary degradation products into bile. J Hepatol. 1993 Jan;17(1):67-73. [PubMed:8445222 ]
  7. Granfors MT, Backman JT, Laitila J, Neuvonen PJ: Oral contraceptives containing ethinyl estradiol and gestodene markedly increase plasma concentrations and effects of tizanidine by inhibiting cytochrome P450 1A2. Clin Pharmacol Ther. 2005 Oct;78(4):400-11. [PubMed:16198659 ]
  8. Blanchard J, Weber CW, Shearer LE: HPLC analysis of methylxanthines in human breast milk. J Chromatogr Sci. 1990 Dec;28(12):640-2. [PubMed:2292610 ]
  9. Delahunty T, Schoendorfer D: Caffeine demethylation monitoring using a transdermal sweat patch. J Anal Toxicol. 1998 Nov-Dec;22(7):596-600. [PubMed:9847011 ]
  10. Holland DT, Godfredsen KA, Page T, Connor JD: Simple high-performance liquid chromatography method for the simultaneous determination of serum caffeine and paraxanthine following rapid sample preparation. J Chromatogr B Biomed Sci Appl. 1998 Apr 10;707(1-2):105-10. [PubMed:9613939 ]
  11. Fuhr U, Rost KL, Engelhardt R, Sachs M, Liermann D, Belloc C, Beaune P, Janezic S, Grant D, Meyer UA, Staib AH: Evaluation of caffeine as a test drug for CYP1A2, NAT2 and CYP2E1 phenotyping in man by in vivo versus in vitro correlations. Pharmacogenetics. 1996 Apr;6(2):159-76. [PubMed:9156694 ]
  12. Zaigler M, Rietbrock S, Szymanski J, Dericks-Tan JS, Staib AH, Fuhr U: Variation of CYP1A2-dependent caffeine metabolism during menstrual cycle in healthy women. Int J Clin Pharmacol Ther. 2000 May;38(5):235-44. [PubMed:10839467 ]
  13. Blanchard J, Weber CW, Shearer LE: Methylxanthine levels in breast milk of lactating women of different ethnic and socioeconomic classes. Biopharm Drug Dispos. 1992 Apr;13(3):187-96. [PubMed:1576327 ]
  14. Wahllander A, Renner E, Karlaganis G: High-performance liquid chromatographic determination of dimethylxanthine metabolites of caffeine in human plasma. J Chromatogr. 1985 Mar 22;338(2):369-75. [PubMed:3998024 ]
  15. Koch JP, ten Tusscher GW, Koppe JG, Guchelaar HJ: Validation of a high-performance liquid chromatography assay for quantification of caffeine and paraxanthine in human serum in the context of CYP1A2 phenotyping. Biomed Chromatogr. 1999 Jun;13(4):309-14. [PubMed:10416066 ]
  16. Sachse C, Ruschen S, Dettling M, Schley J, Bauer S, Muller-Oerlinghausen B, Roots I, Brockmoller J: Flavin monooxygenase 3 (FMO3) polymorphism in a white population: allele frequencies, mutation linkage, and functional effects on clozapine and caffeine metabolism. Clin Pharmacol Ther. 1999 Oct;66(4):431-8. [PubMed:10546928 ]

Only showing the first 10 proteins. There are 28 proteins in total.

Enzymes

General function:
Involved in acetyltransferase activity
Specific function:
Participates in the detoxification of a plethora of hydrazine and arylamine drugs. Catalyzes the N- or O-acetylation of various arylamine and heterocyclic amine substrates and is able to bioactivate several known carcinogens.
Gene Name:
NAT1
Uniprot ID:
P18440
Molecular weight:
33898.445
Reactions
Paraxanthine → 5-Acetylamino-6-formylamino-3-methyluracildetails
General function:
Involved in acetyltransferase activity
Specific function:
Participates in the detoxification of a plethora of hydrazine and arylamine drugs. Catalyzes the N- or O-acetylation of various arylamine and heterocyclic amine substrates and is able to bioactivate several known carcinogens.
Gene Name:
NAT2
Uniprot ID:
P11245
Molecular weight:
33570.245
Reactions
Paraxanthine → 5-Acetylamino-6-formylamino-3-methyluracildetails
General function:
Involved in oxidoreductase activity
Specific function:
Key enzyme in purine degradation. Catalyzes the oxidation of hypoxanthine to xanthine. Catalyzes the oxidation of xanthine to uric acid. Contributes to the generation of reactive oxygen species. Has also low oxidase activity towards aldehydes (in vitro).
Gene Name:
XDH
Uniprot ID:
P47989
Molecular weight:
146422.99
Reactions
Paraxanthine + Oxygen + Water → 1,7-Dimethyluric acid + Hydrogen peroxidedetails
General function:
Involved in monooxygenase activity
Specific function:
Cytochromes P450 are a group of heme-thiolate monooxygenases. In liver microsomes, this enzyme is involved in an NADPH-dependent electron transport pathway. It performs a variety of oxidation reactions (e.g. caffeine 8-oxidation, omeprazole sulphoxidation, midazolam 1'-hydroxylation and midazolam 4-hydroxylation) of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics. Acts as a 1,8-cineole 2-exo-monooxygenase. The enzyme also hydroxylates etoposide.
Gene Name:
CYP3A4
Uniprot ID:
P08684
Molecular weight:
57255.585
General function:
Involved in monooxygenase activity
Specific function:
Cytochromes P450 are a group of heme-thiolate monooxygenases. In liver microsomes, this enzyme is involved in an NADPH-dependent electron transport pathway. It oxidizes a variety of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics. This enzyme contributes to the wide pharmacokinetics variability of the metabolism of drugs such as S-warfarin, diclofenac, phenytoin, tolbutamide and losartan.
Gene Name:
CYP2C9
Uniprot ID:
P11712
Molecular weight:
55627.365
General function:
Involved in monooxygenase activity
Specific function:
Responsible for the metabolism of a number of therapeutic agents such as the anticonvulsant drug S-mephenytoin, omeprazole, proguanil, certain barbiturates, diazepam, propranolol, citalopram and imipramine.
Gene Name:
CYP2C19
Uniprot ID:
P33261
Molecular weight:
55944.565
General function:
Involved in monooxygenase activity
Specific function:
Metabolizes several precarcinogens, drugs, and solvents to reactive metabolites. Inactivates a number of drugs and xenobiotics and also bioactivates many xenobiotic substrates to their hepatotoxic or carcinogenic forms.
Gene Name:
CYP2E1
Uniprot ID:
P05181
Molecular weight:
56848.42
General function:
Involved in monooxygenase activity
Specific function:
Exhibits low testosterone 6-beta-hydroxylase activity.
Gene Name:
CYP3A43
Uniprot ID:
Q9HB55
Molecular weight:
57756.285
General function:
Involved in monooxygenase activity
Specific function:
Cytochromes P450 are a group of heme-thiolate monooxygenases. In liver microsomes, this enzyme is involved in an NADPH-dependent electron transport pathway. It oxidizes a variety of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics. Participates in the metabolism of an as-yet-unknown biologically active molecule that is a participant in eye development.
Gene Name:
CYP1B1
Uniprot ID:
Q16678
Molecular weight:
60845.33
General function:
Involved in monooxygenase activity
Specific function:
Cytochromes P450 are a group of heme-thiolate monooxygenases. In liver microsomes, this enzyme is involved in an NADPH-dependent electron transport pathway. It oxidizes a variety of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics.
Gene Name:
CYP2C18
Uniprot ID:
P33260
Molecular weight:
55710.075

Only showing the first 10 proteins. There are 28 proteins in total.