SBML version of https://gist.github.com/CnrLwlss/7720846

ProtExample.xml

<?xml version="1.0" encoding="UTF-8"?>
<sbml xmlns="http://www.sbml.org/sbml/level2/version3" level="2" version="3">
  <model id="ProteinExample">
    <listOfCompartments>
      <compartment id="cell" size="1"/>
    </listOfCompartments>
    <listOfSpecies>
      <species id="A" compartment="cell" initialAmount="4"/>
      <species id="B" compartment="cell" initialAmount="2"/>
      <species id="AB" compartment="cell" initialAmount="0"/>
      <species id="NULL" compartment="cell" initialAmount="0"/>
    </listOfSpecies>
    <listOfParameters>
      <parameter id="k1" value="0.15"/>
      <parameter id="k2" value="0.075"/>
    </listOfParameters>
    <listOfReactions>
      <reaction id="reaction1" reversible="false">
        <listOfReactants>
          <speciesReference species="A" stoichiometry="1"/>
          <speciesReference species="B" stoichiometry="1"/>
        </listOfReactants>
        <listOfProducts>
          <speciesReference species="AB" stoichiometry="1"/>
        </listOfProducts>
        <kineticLaw>
          <math xmlns="http://www.w3.org/1998/Math/MathML">
            <apply>
              <times/>
              <ci> k1 </ci>
              <ci> A </ci>
              <ci> B </ci>
            </apply>
          </math>
        </kineticLaw>
      </reaction>
      <reaction id="reaction2" reversible="false">
        <listOfReactants>
          <speciesReference species="B" stoichiometry="1"/>
        </listOfReactants>
        <listOfProducts>
          <speciesReference species="NULL" stoichiometry="1"/>
        </listOfProducts>
        <kineticLaw>
          <math xmlns="http://www.w3.org/1998/Math/MathML">
            <apply>
              <times/>
              <ci> k2 </ci>
              <ci> B </ci>
            </apply>
          </math>
        </kineticLaw>
      </reaction>
    </listOfReactions>
  </model>
</sbml>