def extract_isotopes_fractions(isotopes):
    """Extract the list of isotopes and the respective fractions from the MCNP
    parsed composition."""
    fractions = []
    for (enum_element, mass_number), abundance in isotopes:
        if mass_number.startswith('0'):
            mass_number = str(int(mass_number))
        isotope_t4 = enum_element.name + mass_number
        fractions.append((isotope_t4, abundance))
    return fractions
