On the cofactor specificity of glycinamide ribonucleotide and 5-aminoimidazole-4-carboxamide ribonucleotide transformylase from chicken liver

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Abstract
Tests of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) and glycinamide ribonucleotide (GAR) transformylase cofactor specificity were conducted with 5- and/or 8-deazafolate analogs formylated at N-10. Several of these compounds served as cofactors for both the enzymes. The finding that 10-formyl-8-deazafolate can be used by AICAR transformylase eliminates those mechanisms requiring cyclization to a methenyl derivative prior to carbon unit transfer for this transformylase. A similar analog, 10-formyl-5,8-deazafolate, is very effective as a cofactor for GAR transformylase in the presence or absence of the trifunctional protein which is required for 5,10-methenyl-H4-folate activity with this transformylase. Apparently, the trifunctional protein modulates GAR transformylase cofactor specificity by supplying the active cofactor as the N10-formyl species, possibly through a transport process that avoids its dissociation into solution.