    <?xml version="1.0" encoding="UTF-8"?>
    <sbml xmlns="http://www.sbml.org/sbml/level3/version1/core" level="3" version="1"
          xmlns:comp="http://www.sbml.org/sbml/level3/version1/comp/version1" comp:required="true">

      <model id="aggregate">
        <comp:listOfSubmodels>
          <comp:submodel comp:id="submod1" comp:modelRef="enzyme"/>
          <comp:submodel comp:id="submod2" comp:modelRef="enzyme"/>
        </comp:listOfSubmodels>
      </model>
      <comp:listOfModelDefinitions>
        <comp:modelDefinition id="enzyme" name="enzyme">
          <listOfCompartments>
            <compartment id="compartment" spatialDimensions="3" size="1" constant="true"/>
          </listOfCompartments>
          <listOfSpecies>
            <species id="S"  compartment="compartment" hasOnlySubstanceUnits="false"
                             boundaryCondition="false" constant="false"/>
            <species id="E"  compartment="compartment" hasOnlySubstanceUnits="false"
                             boundaryCondition="false" constant="false"/>
            <species id="D"  compartment="compartment" hasOnlySubstanceUnits="false"
                             boundaryCondition="false" constant="false"/>
            <species id="ES" compartment="compartment" hasOnlySubstanceUnits="false"
                             boundaryCondition="false" constant="false"/>
          </listOfSpecies>
          <listOfReactions>
            <reaction id="J0" reversible="true" fast="false">
              <listOfReactants>
                <speciesReference species="S" stoichiometry="1" constant="true"/>
                <speciesReference species="E" stoichiometry="1" constant="true"/>
              </listOfReactants>
              <listOfProducts>
                <speciesReference species="ES" stoichiometry="1" constant="true"/>
              </listOfProducts>
            </reaction>
            <reaction id="J1" reversible="true" fast="false">
              <listOfReactants>
                <speciesReference species="ES" stoichiometry="1" constant="true"/>
              </listOfReactants>
              <listOfProducts>
                <speciesReference species="E" stoichiometry="1" constant="true"/>
                <speciesReference species="D" stoichiometry="1" constant="true"/>
              </listOfProducts>
            </reaction>
          </listOfReactions>
        </comp:modelDefinition>
      </comp:listOfModelDefinitions>
    </sbml>