Biomaterial Database

Mycophenolic acid and thiazole adenine dinucleotide inhibition of Tritrichomonas foetus inosine 5'-monophosphate dehydrogenase: implications on enzyme mechanism. 1990

L Hedstrom, and C C Wang

Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco 94143.

Inosine 5'-monophosphate dehydrogenase (IMPDH) catalyzes the oxidation of inosine 5'-monophosphate (IMP) to xanthosine 5'-monophosphate (XMP) with the conversion of NAD to NADH. An ordered sequential mechanism where IMP is the first substrate bound and XMP is the last product released was proposed for Tritrichomonas foetus IMPDH on the basis of product inhibition studies. Thiazole adenine dinucleotide (TAD) is an uncompetitive inhibitor versus IMP and a noncompetitive inhibitor versus NAD, which suggests that TAD binds to both E-IMP and E-XMP. Mycophenolic acid is also an uncompetitive inhibitor versus IMP and noncompetitive versus NAD. Multiple-inhibitor experiments show that TAD and mycophenolic acid are mutually exclusive with each other and with NADH. Therefore, mycophenolic acid most probably binds to the dinucleotide site of T. foetus IMPDH. The mycophenolic acid binding site was further localized to the nicotinamide subsite within the dinucleotide site: mycophenolic acid was mutually exclusive with tiazofurin, but could form ternary enzyme complexes with ADP or adenosine diphosphate ribose. NAD inhibits the IMPDH reaction at concentrations greater than 3 mM. NAD substrate inhibition is uncompetitive versus IMP, which suggests that NAD inhibits by binding to E-XMP. TAD is mutually exclusive with both NAD and NADH in multiple-inhibitor experiments, which suggests that there is one dinucleotide binding site. The ordered mechanism predicts that multiple-inhibitor experiments with XMP and TAD, mycophenolic acid, or NAD should have an interaction constant (alpha) between 0 and 1. However, alpha was greater than 1 in all cases.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D007168	IMP Dehydrogenase	An enzyme that catalyzes the dehydrogenation of inosine 5'-phosphate to xanthosine 5'-phosphate in the presence of NAD. EC 1.1.1.205.	Inosinic Acid Dehydrogenase,Inosine-5-Monophosphate Dehydrogenase,Acid Dehydrogenase, Inosinic,Dehydrogenase, IMP,Dehydrogenase, Inosine-5-Monophosphate,Dehydrogenase, Inosinic Acid,Inosine 5 Monophosphate Dehydrogenase
D007536	Isomerism	The phenomenon whereby certain chemical compounds have structures that are different although the compounds possess the same elemental composition. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)	Isomerisms
D007658	Ketone Oxidoreductases	Oxidoreductases that are specific for KETONES.	Oxidoreductases, Ketone
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D009173	Mycophenolic Acid	Compound derived from Penicillium stoloniferum and related species. It blocks de novo biosynthesis of purine nucleotides by inhibition of the enzyme inosine monophosphate dehydrogenase (IMP DEHYDROGENASE). Mycophenolic acid exerts selective effects on the immune system in which it prevents the proliferation of T-CELLS, LYMPHOCYTES, and the formation of antibodies from B-CELLS. It may also inhibit recruitment of LEUKOCYTES to sites of INFLAMMATION.	Cellcept,Mycophenolate Mofetil,Mycophenolate Mofetil Hydrochloride,Mycophenolate Sodium,Mycophenolic Acid Morpholinoethyl Ester,Myfortic,RS 61443,RS-61443,Sodium Mycophenolate,Mofetil Hydrochloride, Mycophenolate,Mofetil, Mycophenolate,Mycophenolate, Sodium,RS61443
D009243	NAD	A coenzyme composed of ribosylnicotinamide 5'-diphosphate coupled to adenosine 5'-phosphate by pyrophosphate linkage. It is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH). (Dorland, 27th ed)	Coenzyme I,DPN,Diphosphopyridine Nucleotide,Nadide,Nicotinamide-Adenine Dinucleotide,Dihydronicotinamide Adenine Dinucleotide,NADH,Adenine Dinucleotide, Dihydronicotinamide,Dinucleotide, Dihydronicotinamide Adenine,Dinucleotide, Nicotinamide-Adenine,Nicotinamide Adenine Dinucleotide,Nucleotide, Diphosphopyridine
D000227	Adenine Nucleotides		Adenine Nucleotide,Adenosine Phosphate,Adenosine Phosphates,Nucleotide, Adenine,Nucleotides, Adenine,Phosphate, Adenosine,Phosphates, Adenosine
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D001667	Binding, Competitive	The interaction of two or more substrates or ligands with the same binding site. The displacement of one by the other is used in quantitative and selective affinity measurements.	Competitive Binding