Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.4 (deaminase)
 5,113 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Formiminotransferase-cyclodeaminase denatured in 6 M guanidine hydrochloride (Gdn.HCl) refolds and reassembles to the native octameric structure upon dilution into buffer. Both enzymic activities are recovered to greater than 90%, and the renatured enzyme "channels" the formiminotetrahydropteroylpentaglutamate intermediate. Under conditions where the two activities are recovered simultaneously, the rate-limiting step in reactivation is first order with respect to protein, with k = 1.9 X 10(-5) s-1 at 22 degrees C and delta E approximately equal to 15 kcal mol-1. In the presence of 1.5 M urea, renaturation is arrested at the level of dimers having only transferase activity. Subsequent dialysis to remove the urea leads to recovery of deaminase activity and formation of octamer. Kinetic studies with mono- and pentaglutamate derivatives of the folate substrates demonstrated that native and renatured enzyme as well as deaminase-active dimers [Findlay, W. A., & MacKenzie, R. E (1987) Biochemistry 26, 1948-1954] have much higher affinity for polyglutamate substrates, while the transferase-active dimers do not. These results indicate that the transferase activity is associated with one type of subunit-subunit interaction in the native tetramer of dimers and that the polyglutamate binding site and the deaminase activity are associated with the other interface. A dimeric transferase-active fragment generated by limited proteolysis of the native enzyme can also be renatured from 6 M Gdn.HCl, confirming that it is an independently folding domain capable of reforming one type of subunit interaction.
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PMID:Renaturation of formiminotransferase-cyclodeaminase from guanidine hydrochloride. Quaternary structure requirements for the activities and polyglutamate specificity. 339 Apr 40

Formiminotransferase-cyclodeaminase, a circular tetramer of dimers, binds four tetrahydropteroylpolyglutamates/octamer, which indicates that these polyglutamate sites are formed by one type of subunit interface. The transferase and deaminase are separate catalytic sites as determined by inhibition studies with (6R)-tetrahydropteroylglutamate and by the observation that the activities can operate simultaneously. Under conditions where the transferase is saturated with tetrahydropteroyl(glutamate)n substrate, exogenously added formimino intermediate is utilized by the deaminase only if at least one of the substrate/intermediate pair is a monoglutamate. These properties indicate the existence of only one polyglutamate site/pair of catalytic sites. Kinetic specificity for each activity as measured by Vm/Km increases for longer polyglutamates, but does not differentiate among 4, 5, 6, and 7 glutamates. The enzyme shows distinct preference for hexaglutamate based on Kd as well as on Km values. With all substrates, Vm of the deaminase is greater than that of the transferase, allowing for potential channeling of the intermediate between active sites. Efficiency of channeling, optimal with pentaglutamate, does not correspond with affinity for binding. This demonstrates that a steric requirement predominates over simple sequestering of intermediates on the enzyme surface as the fundamental mechanism for channeling.
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PMID:Channeling between the active sites of formiminotransferase-cyclodeaminase. Binding and kinetic studies. 406 60

Formiminotransferase-cyclodeaminase, an octameric protein of identical, bifunctional polypeptides of Mr = 62,000, yields a transferase-active fragment of Mr = 80,000 upon proteolysis with chymotrypsin in the presence of the inhibitor folic acid. The purified fragment contains one size of polypeptide, Mr = 39,000, on dodecyl sulfate gels. Cross-linking with the bifunctional reagent dithiobis(succinimidyl propionate) confirmed the dimeric structure of the purified fragment. Reaction of the native octamer with the very short bifunctional reagent difluorodinitrobenzene yields dimer and tetramer in excess of trimer, thereby indicating two types of subunit interaction in the protein. The isolation of a dimeric fragment after proteolysis and the results of cross-linking support a tetramer of dimers structure for the native enzyme. The purified transferase fragment has approximately 68% of the activity of the native enzyme, but has lost specificity for the naturally occurring polyglutamate derivatives of tetrahydrofolate. This is illustrated by an increase in Km for tetrahydropteroylpentaglutamate from 3.4 microM with the native transferase to 89 microM with the fragment transferase. It is suggested that the bifunctional enzyme may have only one polyglutamate binding site/pair of transferase-deaminase sites.
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PMID:The bifunctional enzyme formiminotransferase-cyclodeaminase is a tetramer of dimers. 741 Apr 36

Formiminotransferase-cyclodeaminase is a bifunctional enzyme arranged as a circular tetramer of dimers that exhibits the ability to efficiently channel polyglutamylated folate between catalytic sites. Through deletion mutagenesis we demonstrate that each subunit consists of an N-terminal transferase active domain and a C-terminal deaminase active domain separated by a linker sequence of minimally eight residues. The full-length enzyme and both isolated domains have been expressed as C-terminally histidine-tagged proteins. Both domains self-dimerize, providing direct evidence for the existence of two types of subunit interfaces. The results suggest that both the transferase and the deaminase activities are dependent on the formation of specific subunit interfaces. Because channeling is not observed between isolated domains, only the octamer appears able to directly transfer pentaglutamylated intermediate between active sites.
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PMID:The two monofunctional domains of octameric formiminotransferase-cyclodeaminase exist as dimers. 765 89