Returns the molar extinction coefficient of the sequence at 280 nm.

    Notes
    -----
    Units = M/cm

    Parameters
    ----------
    seq : str
        Sequence of amino acids.

def sequence_molar_extinction_280(seq):
    """Returns the molar extinction coefficient of the sequence at 280 nm.

    Notes
    -----
    Units = M/cm

    Parameters
    ----------
    seq : str
        Sequence of amino acids.
    """
    if 'X' in seq:
        warnings.warn(_nc_warning_str, NoncanonicalWarning)
    return sum([residue_ext_280[aa] * n for aa, n in Counter(seq).items()])