Action of the active metabolites of tiazofurin and ribavirin on purified IMP dehydrogenase
- 22 March 1988
- journal article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 27 (6), 2193-2196
- https://doi.org/10.1021/bi00406a057
Abstract
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.Keywords
This publication has 16 references indexed in Scilit:
- Purification of IMP dehydrogenase from rat hepatoma 3924ALife Sciences, 1987
- Direct assay method for inosine 5′-monophosphate dehydrogenase activityAnalytical Biochemistry, 1985
- Ribavirin, tiazofurin, and selenazofurin: mononucleotides and nicotinamide adenine dinucleotide analogs. Synthesis, structure, and interactions with IMP dehydrogenaseJournal of Medicinal Chemistry, 1985
- Synergistic antiviral effects of ribavirin and the C-nucleoside analogs tiazofurin and selenazofurin against togaviruses, bunyaviruses, and arenavirusesAntimicrobial Agents and Chemotherapy, 1984
- Inhibition of inosinate dehydrogenase by metabolites of 2-β-D-ribofuranosylthiazole-4-car☐amideBiochemical and Biophysical Research Communications, 1982
- A simplified ultrasensitive silver stain for detecting proteins in polyacrylamide gelsAnalytical Biochemistry, 1980
- Partial purification, properties and regulation of inosine 5′-phosphate dehydrogenase in normal and malignant rat tissuesBiochemical Journal, 1977
- Human IMP dehydrogenase: Kinetics and regulatory propertiesBiochimica et Biophysica Acta (BBA) - Enzymology, 1974
- Cleavage of Structural Proteins during the Assembly of the Head of Bacteriophage T4Nature, 1970
- The kinetics of enzyme-catalyzed reactions with two or more substrates or productsBiochimica et Biophysica Acta (BBA) - Specialized Section on Enzymological Subjects, 1963