def calcMassFromMz(mz, charge):
    """Calculate the mass of a peptide from its mz and charge.

    :param mz: float, mass to charge ratio (Dalton / charge)
    :param charge: int, charge state

    :returns: non protonated mass (charge = 0)
    """
    mass = (mz - maspy.constants.atomicMassProton) * charge
    return mass