[Koha] MARC 001 Field

In the MARC 21 code there is the 001 field, which is the unequivocal idetifier of each record. However, I can't find any support for this field in Koha (for ex. a script which fills this field authomatically). Could anyone tell me how does this field function in Koha? It seems that Koha uses rather some of the 999 subfields for the unequivoque identifiing. Is therefore sme way how to map the Koha field in 001 MARC field? Or, in Koha is it prefered not to use this field?... Thank you in advance Ondrej Mlecka Casa Balthasar Rome