Purine biosynthesis in the domain Archaea without folates or modified folates.

The established pathway for the last two steps in purine biosynthesis, the conversion of 5-aminoimidazole-4-carboxamide ribonucleotide (ZMP) to IMP, is known to utilize 10-formyl-tetrahydrofolate as the required C1 donor cofactor. The biosynthetic conversion of ZMP to IMP in three members of the domain Archaea, Methanobacterium thermoautotrophicum deltaH, M. thermoautotrophicum Marburg, and Sulfolobus solfataricus, however, has been demonstrated to occur with only formate and ATP serving as cofactors. Thus, in these archaea, which use methanopterin (MPT) or another modified folate in place of folate as the C1 carrier coenzyme, neither folate nor a modified folate serves as a cofactor for this biosynthetic transformation. It is concluded that archaea, which function with modified folates such as MPT, are able to carry out purine biosynthesis without the involvement of folates or modified folates.