[gmx-users] how to connect ligating residues?

[Shumaila Khan]

Hello Sir,
        Hopefully you are doing well. As I am new to GROMACS, I am facing problems.
I read your comments and You suggested someone that "You should not need external servers to generate a heme topology; GROMOS already supports it.  It's called HEME and it's in the .rtp file.  Connections to
ligating residues should be recognized via existing entries in specbond.dat."
I am using
Version : 5.0.7
Force Feild : 43a1 Spc water model.
The  ligand  attached to heme is oxygen molecule.
HETATM 1  O1  OXY C1543      5.525  80.353  -6.212  1.00 25.38  O
HETATM 2  O2  OXY C1543      4.301  80.342  -6.721  1.00 30.35  O
END

The specbond.dat file contains the following:
8
CYS    SG    1    CYS    SG    1    0.2    CYS2    CYS2
CYS    SG    1    HEM    FE    2    0.25    CYS2    HEME
CYS    SG    1    HEM    CAB    1    0.18    CYS2    HEME
CYS    SG    1    HEM    CAC    1    0.18    CYS2    HEME
HIS    NE2    1    HEM    FE    1    0.2    HIS1    HEME
MET    SD    1    HEM    FE    1    0.24    MET    HEME
CO  C      1      HEME    FE      1      0.19    CO      HEME
CYM  SG      1      CYM    SG      1      0.2    CYS2    CYS2
 

Kindly please guide me, how connections to ligating residues should be recognized via existing entries in specbond.dat?

 I shall be very thankful to you.
                                                                        Shumaila khan