def _get_enzrnx_to_sequence_mapping(enzrxn_to_monomer, sequences):
    """Get mapping of enzyme reactions to sequences."""
    enzrxn_to_sequence = {}
    for enzrxn, monomers in enzrxn_to_monomer.items():
        for monomer in monomers:
            try:
                sequence = sequences[monomer]
                enzrxn_to_sequence.setdefault(enzrxn, dict())[monomer
                    ] = sequence
            except KeyError:
                pass
    return enzrxn_to_sequence
