RGD Reference Report - Action of the active metabolites of tiazofurin and ribavirin on purified IMP dehydrogenase. - Rat Genome Database

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Action of the active metabolites of tiazofurin and ribavirin on purified IMP dehydrogenase.

Authors: Yamada, Y  Natsumeda, Y  Weber, G 
Citation: Yamada Y, etal., Biochemistry. 1988 Mar 22;27(6):2193-6.
RGD ID: 5147398
Pubmed: PMID:2897864   (View Abstract at PubMed)

The inhibitory mechanisms of ribavirin 5'-monophosphate (RMP) and thiazole-4-carboxamide adenine dinucleotide (TAD), the active forms of the antimetabolites ribavirin and tiazofurin, were investigated in IMP dehydrogenase purified to homogeneity from rat hepatoma 3924A. The hepatoma IMP dehydrogenase has a tetrameric structure with a subunit molecular weight of 60,000. For the substrates IMP and NAD+, Km's were 23 and 65 microM, respectively. Product-inhibition patterns showed an ordered Bi-Bi mechanism for the enzyme reaction where IMP binds to the enzyme first, followed by NAD+; NADH dissociates from the ternary complex first and then XMP is released. XMP interacts with the free enzyme and competes for the ligand site with IMP, while NADH binds to the enzyme-XMP complex. RMP exerted the same inhibitory mechanisms as XMP, and the inhibition by TAD was similar to that by NADH. However, the Ki values for RMP (0.8 microM) and TAD (0.13 microM) were orders of magnitude lower than those of XMP (136 microM) and NADH (210 microM). Thus, the drugs interact with IMP dehydrogenase with higher affinities than the natural substrates and products, RMP with the IMP-XMP site and TAD with the NADH site. Preincubation of the purified enzyme with RMP enhanced its inhibitory effect in a time-dependent manner. The enzyme was protected from this inactivation by IMP or XMP. These results provide a biochemical basis for combination chemotherapy with tiazofurin and ribavirin targeted against the two different ligand sites of IMP dehydrogenase.



Gene Ontology Annotations    Click to see Annotation Detail View

Molecular Function

  
Object SymbolSpeciesTermQualifierEvidenceWithNotesSourceOriginal Reference(s)
Impdh2Ratidentical protein binding  IPIImpdh2 (Rattus norvegicus)homotetramerizationRGD 
Impdh2RatIMP dehydrogenase activity  IDA  RGD 

Objects Annotated

Genes (Rattus norvegicus)
Impdh2  (inosine monophosphate dehydrogenase 2)


Additional Information