<?xml version="1.0" encoding="UTF-8"?>
<metabolite>
  <version>1.0</version>
  <creation_date>2016-09-30 22:49:55 UTC</creation_date>
  <update_date>2020-06-04 20:04:02 UTC</update_date>
  <accession>BMDB0002013</accession>
  <secondary_accessions>
    <accession>BMDB02013</accession>
  </secondary_accessions>
  <name>Butyrylcarnitine</name>
  <description>Butyrylcarnitine, also known as O-butanoylcarnitine, belongs to the class of organic compounds known as acyl carnitines. These are organic compounds containing a fatty acid with the carboxylic acid attached to carnitine through an ester bond. Thus, butyrylcarnitine is considered to be a fatty ester lipid molecule. Butyrylcarnitine is a very hydrophobic molecule, practically insoluble (in water), and relatively neutral. Butyrylcarnitine exists in all eukaryotes, ranging from yeast to humans. Butyrylcarnitine is a potentially toxic compound. Butyrylcarnitine has been found to be associated with several diseases known as obesity, eosinophilic esophagitis, and pregnancy; also butyrylcarnitine has been linked to several inborn metabolic disorders including short chain acyl-coa dehydrogenase deficiency and very long chain acyl-coa dehydrogenase deficiency.</description>
  <synonyms>
    <synonym>(3R)-3-(Butyryloxy)-4-(trimethylammonio)butanoate</synonym>
    <synonym>Butyryl-L-carnitine</synonym>
    <synonym>L-Carnitine butyryl ester</synonym>
    <synonym>N-Butyryl-L-(-)-carnitin</synonym>
    <synonym>O-Butanoyl-(R)-carnitine</synonym>
    <synonym>(3R)-3-(Butyryloxy)-4-(trimethylammonio)butanoic acid</synonym>
    <synonym>Butylcarnitine</synonym>
    <synonym>O-Butanoyl-carnitine</synonym>
    <synonym>O-Butanoylcarnitine</synonym>
    <synonym>Butyrylcarnitine</synonym>
  </synonyms>
  <chemical_formula>C11H21NO4</chemical_formula>
  <average_molecular_weight>231.292</average_molecular_weight>
  <monisotopic_moleculate_weight>231.14705816</monisotopic_moleculate_weight>
  <iupac_name>(3R)-3-(butanoyloxy)-4-(trimethylazaniumyl)butanoate</iupac_name>
  <traditional_iupac>O-butanoylcarnitine</traditional_iupac>
  <cas_registry_number>25576-40-3</cas_registry_number>
  <smiles>CCCC(=O)O[C@H](CC([O-])=O)C[N+](C)(C)C</smiles>
  <inchi>InChI=1S/C11H21NO4/c1-5-6-11(15)16-9(7-10(13)14)8-12(2,3)4/h9H,5-8H2,1-4H3/t9-/m1/s1</inchi>
  <inchikey>QWYFHHGCZUCMBN-SECBINFHSA-N</inchikey>
  <taxonomy>
    <description> belongs to the class of organic compounds known as acyl carnitines. These are organic compounds containing a fatty acid with the carboxylic acid attached to carnitine through an ester bond.</description>
    <kingdom>Organic compounds</kingdom>
    <super_class>Lipids and lipid-like molecules</super_class>
    <class>Fatty Acyls</class>
    <sub_class>Fatty acid esters</sub_class>
    <direct_parent>Acyl carnitines</direct_parent>
    <alternative_parents>
      <alternative_parent>Amines</alternative_parent>
      <alternative_parent>Carbonyl compounds</alternative_parent>
      <alternative_parent>Carboxylic acid esters</alternative_parent>
      <alternative_parent>Carboxylic acid salts</alternative_parent>
      <alternative_parent>Carboxylic acids</alternative_parent>
      <alternative_parent>Dicarboxylic acids and derivatives</alternative_parent>
      <alternative_parent>Hydrocarbon derivatives</alternative_parent>
      <alternative_parent>Organic oxides</alternative_parent>
      <alternative_parent>Organic salts</alternative_parent>
      <alternative_parent>Organopnictogen compounds</alternative_parent>
      <alternative_parent>Tetraalkylammonium salts</alternative_parent>
    </alternative_parents>
    <substituents>
      <substituent>Acyl-carnitine</substituent>
      <substituent>Aliphatic acyclic compound</substituent>
      <substituent>Amine</substituent>
      <substituent>Carbonyl group</substituent>
      <substituent>Carboxylic acid</substituent>
      <substituent>Carboxylic acid derivative</substituent>
      <substituent>Carboxylic acid ester</substituent>
      <substituent>Carboxylic acid salt</substituent>
      <substituent>Dicarboxylic acid or derivatives</substituent>
      <substituent>Hydrocarbon derivative</substituent>
      <substituent>Organic nitrogen compound</substituent>
      <substituent>Organic oxide</substituent>
      <substituent>Organic oxygen compound</substituent>
      <substituent>Organic salt</substituent>
      <substituent>Organonitrogen compound</substituent>
      <substituent>Organooxygen compound</substituent>
      <substituent>Organopnictogen compound</substituent>
      <substituent>Quaternary ammonium salt</substituent>
      <substituent>Tetraalkylammonium salt</substituent>
    </substituents>
    <molecular_framework>Aliphatic acyclic compounds</molecular_framework>
    <external_descriptors>
      <external_descriptor>Fatty acyl carnitines</external_descriptor>
      <external_descriptor>O-butanoylcarnitine</external_descriptor>
    </external_descriptors>
  </taxonomy>
  <experimental_properties>
    <state>Solid</state>
  </experimental_properties>
  <predicted_properties>
    <property>
      <kind>logp</kind>
      <value>-2.10</value>
      <source>ALOGPS</source>
    </property>
    <property>
      <kind>logs</kind>
      <value>-3.74</value>
      <source>ALOGPS</source>
    </property>
    <property>
      <kind>logp</kind>
      <value>-3.3</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>pka_strongest_acidic</kind>
      <value>4.27</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>pka_strongest_basic</kind>
      <value>-7.1</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>iupac</kind>
      <value>(3R)-3-(butanoyloxy)-4-(trimethylazaniumyl)butanoate</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>average_mass</kind>
      <value>231.292</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>mono_mass</kind>
      <value>231.14705816</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>smiles</kind>
      <value>CCCC(=O)O[C@H](CC([O-])=O)C[N+](C)(C)C</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>formula</kind>
      <value>C11H21NO4</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>inchi</kind>
      <value>InChI=1S/C11H21NO4/c1-5-6-11(15)16-9(7-10(13)14)8-12(2,3)4/h9H,5-8H2,1-4H3/t9-/m1/s1</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>inchikey</kind>
      <value>QWYFHHGCZUCMBN-SECBINFHSA-N</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>polar_surface_area</kind>
      <value>66.43</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>refractivity</kind>
      <value>81.86</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>polarizability</kind>
      <value>24.8</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>rotatable_bond_count</kind>
      <value>8</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>acceptor_count</kind>
      <value>3</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>donor_count</kind>
      <value>0</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>physiological_charge</kind>
      <value>0</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>formal_charge</kind>
      <value>0</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>number_of_rings</kind>
      <value>0</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>bioavailability</kind>
      <value>1</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>rule_of_five</kind>
      <value>Yes</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>ghose_filter</kind>
      <value>Yes</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>veber_rule</kind>
      <value>Yes</value>
      <source>ChemAxon</source>
    </property>
    <property>
      <kind>mddr_like_rule</kind>
      <value>Yes</value>
      <source>ChemAxon</source>
    </property>
  </predicted_properties>
  <pathways>
  </pathways>
  <spectra>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2235894</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2237504</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2237952</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2239604</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2239979</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2241751</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2447274</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2447275</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::MsMs</type>
      <spectrum_id>2447276</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::CMs</type>
      <spectrum_id>161674</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148720</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148721</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148722</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148723</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148724</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148725</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148726</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148727</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148728</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148729</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148730</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148731</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148732</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148733</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148734</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148735</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148736</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148737</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148738</spectrum_id>
    </spectrum>
    <spectrum>
      <type>Specdb::NmrOneD</type>
      <spectrum_id>148739</spectrum_id>
    </spectrum>
  </spectra>
  <normal_concentrations>
    <concentration>
      <biospecimen>Blood</biospecimen>
      <concentration_value>0.2 +/- 0.1</concentration_value>
      <concentration_units>uM</concentration_units>
      <comment>By LC-MS/MS</comment>
      <references>
        <reference>
          <reference_text>Aidin Foroutan, Carolyn Fitzsimmons, Rupasri Mandal, Hamed Piri‐Moghadam, Jiamin Zheng, AnChi Guo, Carin Li, Le Luo Guan and David S. Wishart. The Bovine Metabolome. Metabolites 2020, 10, 233; doi:10.3390/metabo10060233</reference_text>
          <pubmed_id/>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Blood</biospecimen>
      <concentration_value/>
      <concentration_units/>
      <comment>Detected by DFI-MS/MS (P180) in periparturient Holstein cows.</comment>
      <references>
        <reference>
          <reference_text>Hailemariam D, Mandal R, Saleem F, Dunn SM, Wishart DS, Ametaj BN: Identification of predictive biomarkers of disease state in transition dairy cows. J Dairy Sci. 2014 May;97(5):2680-93. doi: 10.3168/jds.2013-6803. Epub 2014 Mar 13.</reference_text>
          <pubmed_id>24630653</pubmed_id>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Fibroblasts</biospecimen>
      <concentration_value/>
      <concentration_units/>
      <references>
        <reference>
          <reference_text>Wishart DS, Feunang YD, Marcu A, Guo AC, Liang K, Vazquez-Fresno R, Sajed T, Johnson D, Li C, Karu N, Sayeeda Z, Lo E, Assempour N, Berjanskii M, Singhal S, Arndt D, Liang Y, Badran H, Grant J, Serra-Cayuela A, Liu Y, Mandal R, Neveu V, Pon A, Knox C, Wilson M, Manach C, Scalbert A: HMDB 4.0: the human metabolome database for 2018. Nucleic Acids Res. 2018 Jan 4;46(D1):D608-D617. doi: 10.1093/nar/gkx1089.</reference_text>
          <pubmed_id>29140435</pubmed_id>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Liver</biospecimen>
      <concentration_value>0.36 +/- 0.08</concentration_value>
      <concentration_units>nmol/g of tissue</concentration_units>
      <comment>By LC-MS/MS</comment>
      <references>
        <reference>
          <reference_text>Aidin Foroutan, Carolyn Fitzsimmons, Rupasri Mandal, Hamed Piri‐Moghadam, Jiamin Zheng, AnChi Guo, Carin Li, Le Luo Guan and David S. Wishart. The Bovine Metabolome. Metabolites 2020, 10, 233; doi:10.3390/metabo10060233</reference_text>
          <pubmed_id/>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Longissimus Thoracis Muscle</biospecimen>
      <concentration_value>16 +/- 6</concentration_value>
      <concentration_units>nmol/g of tissue</concentration_units>
      <comment>By LC-MS/MS</comment>
      <references>
        <reference>
          <reference_text>Aidin Foroutan, Carolyn Fitzsimmons, Rupasri Mandal, Hamed Piri‐Moghadam, Jiamin Zheng, AnChi Guo, Carin Li, Le Luo Guan and David S. Wishart. The Bovine Metabolome. Metabolites 2020, 10, 233; doi:10.3390/metabo10060233</reference_text>
          <pubmed_id/>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Milk</biospecimen>
      <concentration_value/>
      <concentration_units/>
      <comment>By GC-MS and LC-MS/MS</comment>
      <references>
        <reference>
          <reference_text>Characterization of the biochemical variability of bovine milk using metabolomics</reference_text>
          <pubmed_id/>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Milk</biospecimen>
      <concentration_value/>
      <concentration_units/>
      <comment>Commercial, conventional whole milk</comment>
      <references>
        <reference>
          <reference_text>Kurt J. Boudonck, Matthew W. Mitchell, Jacob Wulff, John A. Ryals. Characterization of the biochemical variability of bovine milk using metabolomics. Metabolomics (2009) 5:375-386   doi: 10.1007/s11306-009-0160-8</reference_text>
          <pubmed_id/>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Milk</biospecimen>
      <concentration_value>4.4 +/- 0.2</concentration_value>
      <concentration_units>uM</concentration_units>
      <comment>Commercial 1% milk by LC-HRMS</comment>
      <references>
        <reference>
          <reference_text>Foroutan A, Guo AC, Vazquez-Fresno R, Lipfert M, Zhang L, Zheng J, Badran H, Budinski Z, Mandal R, Ametaj BN, Wishart DS: Chemical Composition of Commercial Cow's Milk. J Agric Food Chem. 2019 Apr 17. doi: 10.1021/acs.jafc.9b00204.</reference_text>
          <pubmed_id>30994344</pubmed_id>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Milk</biospecimen>
      <concentration_value>5.8 +/- 0.1</concentration_value>
      <concentration_units>uM</concentration_units>
      <comment>Commercial 2% milk by LC-HRMS</comment>
      <references>
        <reference>
          <reference_text>Foroutan A, Guo AC, Vazquez-Fresno R, Lipfert M, Zhang L, Zheng J, Badran H, Budinski Z, Mandal R, Ametaj BN, Wishart DS: Chemical Composition of Commercial Cow's Milk. J Agric Food Chem. 2019 Apr 17. doi: 10.1021/acs.jafc.9b00204.</reference_text>
          <pubmed_id>30994344</pubmed_id>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Milk</biospecimen>
      <concentration_value>6.6 +/- 0.1</concentration_value>
      <concentration_units>uM</concentration_units>
      <comment>Commercial 3.25% milk by LC-HRMS</comment>
      <references>
        <reference>
          <reference_text>Foroutan A, Guo AC, Vazquez-Fresno R, Lipfert M, Zhang L, Zheng J, Badran H, Budinski Z, Mandal R, Ametaj BN, Wishart DS: Chemical Composition of Commercial Cow's Milk. J Agric Food Chem. 2019 Apr 17. doi: 10.1021/acs.jafc.9b00204.</reference_text>
          <pubmed_id>30994344</pubmed_id>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Milk</biospecimen>
      <concentration_value>3.99 +/- 0.04</concentration_value>
      <concentration_units>uM</concentration_units>
      <comment>Commercial skim milk by LC-HRMS</comment>
      <references>
        <reference>
          <reference_text>Foroutan A, Guo AC, Vazquez-Fresno R, Lipfert M, Zhang L, Zheng J, Badran H, Budinski Z, Mandal R, Ametaj BN, Wishart DS: Chemical Composition of Commercial Cow's Milk. J Agric Food Chem. 2019 Apr 17. doi: 10.1021/acs.jafc.9b00204.</reference_text>
          <pubmed_id>30994344</pubmed_id>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Placenta</biospecimen>
      <concentration_value/>
      <concentration_units/>
      <references>
        <reference>
          <reference_text>Wishart DS, Feunang YD, Marcu A, Guo AC, Liang K, Vazquez-Fresno R, Sajed T, Johnson D, Li C, Karu N, Sayeeda Z, Lo E, Assempour N, Berjanskii M, Singhal S, Arndt D, Liang Y, Badran H, Grant J, Serra-Cayuela A, Liu Y, Mandal R, Neveu V, Pon A, Knox C, Wilson M, Manach C, Scalbert A: HMDB 4.0: the human metabolome database for 2018. Nucleic Acids Res. 2018 Jan 4;46(D1):D608-D617. doi: 10.1093/nar/gkx1089.</reference_text>
          <pubmed_id>29140435</pubmed_id>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Ruminal Fluid</biospecimen>
      <concentration_value>0.05 +/- 0.02</concentration_value>
      <concentration_units>uM</concentration_units>
      <comment>By LC-MS/MS</comment>
      <references>
        <reference>
          <reference_text>Aidin Foroutan, Carolyn Fitzsimmons, Rupasri Mandal, Hamed Piri‐Moghadam, Jiamin Zheng, AnChi Guo, Carin Li, Le Luo Guan and David S. Wishart. The Bovine Metabolome. Metabolites 2020, 10, 233; doi:10.3390/metabo10060233</reference_text>
          <pubmed_id/>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Semimembranosus Muscle</biospecimen>
      <concentration_value>22 +/- 8</concentration_value>
      <concentration_units>nmol/g of tissue</concentration_units>
      <comment>By LC-MS/MS</comment>
      <references>
        <reference>
          <reference_text>Aidin Foroutan, Carolyn Fitzsimmons, Rupasri Mandal, Hamed Piri‐Moghadam, Jiamin Zheng, AnChi Guo, Carin Li, Le Luo Guan and David S. Wishart. The Bovine Metabolome. Metabolites 2020, 10, 233; doi:10.3390/metabo10060233</reference_text>
          <pubmed_id/>
        </reference>
      </references>
    </concentration>
    <concentration>
      <biospecimen>Testis</biospecimen>
      <concentration_value>2.8 +/- 0.7</concentration_value>
      <concentration_units>nmol/g of tissue</concentration_units>
      <comment>By LC-MS/MS</comment>
      <references>
        <reference>
          <reference_text>Aidin Foroutan, Carolyn Fitzsimmons, Rupasri Mandal, Hamed Piri‐Moghadam, Jiamin Zheng, AnChi Guo, Carin Li, Le Luo Guan and David S. Wishart. The Bovine Metabolome. Metabolites 2020, 10, 233; doi:10.3390/metabo10060233</reference_text>
          <pubmed_id/>
        </reference>
      </references>
    </concentration>
  </normal_concentrations>
  <foodb_id>FDB022795</foodb_id>
  <pubchem_compound_id>213144</pubchem_compound_id>
  <chemspider_id>184820</chemspider_id>
  <chebi_id>21949</chebi_id>
  <kegg_id>C02862</kegg_id>
  <drugbank_id/>
  <knapsack_id>C00052220</knapsack_id>
  <pdbe_id/>
  <meta_cyc_id/>
  <phenol_explorer_compound_id/>
  <bigg_id/>
  <wikipedia_id/>
  <metlin_id>6436</metlin_id>
  <synthesis_reference>Lozano Pedro; Daz Mirta; de Diego Teresa; Iborra Jose L  Ester synthesis from trimethylammonium alcohols in dry organic media catalyzed by immobilized Candida antarctica lipase B.    Biotechnology and bioengineering  (2003),  82(3),  352-8.</synthesis_reference>
  <general_references>
    <reference>
      <reference_text>Kurt J. Boudonck, Matthew W. Mitchell, Jacob Wulff and John A. Ryals. Characterization of the biochemical variability of bovine milk using metabolomics. Metabolomics (2009) 5:375?386</reference_text>
    </reference>
    <reference>
      <reference_text>Characterization of the biochemical variability of bovine milk using metabolomics</reference_text>
    </reference>
    <reference>
      <reference_text>A. Foroutan et al. The Chemical Composition of Commercial Cow's Milk (in preparation)</reference_text>
    </reference>
  </general_references>
  <protein_associations>
  </protein_associations>
</metabolite>
