Enzymes
UniProtKB help_outline | 4 proteins |
Enzyme class help_outline |
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- Name help_outline mercaptopurine Identifier CHEBI:50667 (Beilstein: 132916; CAS: 50-44-2) help_outline Charge 0 Formula C5H4N4S InChIKeyhelp_outline GLVAUDGFNGKCSF-UHFFFAOYSA-N SMILEShelp_outline S=c1[nH]cnc2nc[nH]c12 2D coordinates Mol file for the small molecule Search links Involved in 1 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline S-adenosyl-L-methionine Identifier CHEBI:59789 Charge 1 Formula C15H23N6O5S InChIKeyhelp_outline MEFKEPWMEQBLKI-AIRLBKTGSA-O SMILEShelp_outline C[S+](CC[C@H]([NH3+])C([O-])=O)C[C@H]1O[C@H]([C@H](O)[C@@H]1O)n1cnc2c(N)ncnc12 2D coordinates Mol file for the small molecule Search links Involved in 842 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline 6-methylthiopurine Identifier CHEBI:28279 (CAS: 50-66-8) help_outline Charge 0 Formula C6H6N4S InChIKeyhelp_outline UIJIQXGRFSPYQW-UHFFFAOYSA-N SMILEShelp_outline CSc1ncnc2[nH]cnc12 2D coordinates Mol file for the small molecule Search links Involved in 1 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline H+ Identifier CHEBI:15378 Charge 1 Formula H InChIKeyhelp_outline GPRLSGONYQIRFK-UHFFFAOYSA-N SMILEShelp_outline [H+] 2D coordinates Mol file for the small molecule Search links Involved in 9,176 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
- Name help_outline S-adenosyl-L-homocysteine Identifier CHEBI:57856 Charge 0 Formula C14H20N6O5S InChIKeyhelp_outline ZJUKTBDSGOFHSH-WFMPWKQPSA-N SMILEShelp_outline Nc1ncnc2n(cnc12)[C@@H]1O[C@H](CSCC[C@H]([NH3+])C([O-])=O)[C@@H](O)[C@H]1O 2D coordinates Mol file for the small molecule Search links Involved in 768 reaction(s) Find molecules that contain or resemble this structure Find proteins in UniProtKB for this molecule
Cross-references
RHEA:12609 | RHEA:12610 | RHEA:12611 | RHEA:12612 | |
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Reaction direction help_outline | undefined | left-to-right | right-to-left | bidirectional |
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Publications
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Structural basis of substrate recognition in thiopurine S-methyltransferase.
Peng Y., Feng Q., Wilk D., Adjei A.A., Salavaggione O.E., Weinshilboum R.M., Yee V.C.
Thiopurine S-methyltransferase (TPMT) modulates the cytotoxic effects of thiopurine prodrugs such as 6-mercaptopurine by methylating them in a reaction using S-adenosyl-l-methionine as the donor. Patients with TPMT variant allozymes exhibit diminished levels of protein and/or enzyme activity and a ... >> More
Thiopurine S-methyltransferase (TPMT) modulates the cytotoxic effects of thiopurine prodrugs such as 6-mercaptopurine by methylating them in a reaction using S-adenosyl-l-methionine as the donor. Patients with TPMT variant allozymes exhibit diminished levels of protein and/or enzyme activity and are at risk for thiopurine drug-induced toxicity. We have determined two crystal structures of murine TPMT, as a binary complex with the product S-adenosyl-l-homocysteine and as a ternary complex with S-adenosyl-l-homocysteine and the substrate 6-mercaptopurine, to 1.8 and 2.0 A resolution, respectively. Comparison of the structures reveals that an active site loop becomes ordered upon 6-mercaptopurine binding. The positions of the two ligands are consistent with the expected S N2 reaction mechanism. Arg147 and Arg221, the only polar amino acids near 6-mercaptopurine, are highlighted as possible participants in substrate deprotonation. To probe whether these residues are important for catalysis, point mutants were prepared in the human enzyme. Substitution of Arg152 (Arg147 in murine TPMT) with glutamic acid decreases V max and increases K m for 6-mercaptopurine but not K m for S-adenosyl-l-methionine. Substitution at this position with alanine or histidine and similar substitutions of Arg226 (Arg221 in murine TPMT) result in no effect on enzyme activity. The double mutant Arg152Ala/Arg226Ala exhibits a decreased V max and increased K m for 6-mercaptopurine. These observations suggest that either Arg152 or Arg226 may participate in some fashion in the TPMT reaction, with one residue compensating when the other is altered, and that Arg152 may interact with substrate more directly than Arg226, consistent with observations in the murine TPMT crystal structure. << Less
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Human erythrocyte thiopurine methyltransferase: radiochemical microassay and biochemical properties.
Weinshilboum R.M., Raymond F.A., Pazmino P.A.
A radiochemical micromethod for the determination of thiopurine methyltransferase (TPMT) activity in human red blood cells (RBC) is described. Both 6-mercaptopurine and 6-thioguanine were substrates for the TPMT activity in the human RBC. Apparent Michaelis-Menten (KM) values for 6-mercaptopurine ... >> More
A radiochemical micromethod for the determination of thiopurine methyltransferase (TPMT) activity in human red blood cells (RBC) is described. Both 6-mercaptopurine and 6-thioguanine were substrates for the TPMT activity in the human RBC. Apparent Michaelis-Menten (KM) values for 6-mercaptopurine and 6-thioguanine were 3.2 X 10(-4) M and 2.0 X 10(-4) M, respectively. The apparent KM value for S-adenosyl-L-methionine, a co-substrate for the reaction, was 1.7 X 10(-6) M. The pH optimum for the reaction was approximately 7.5. Blood samples from 73 randomly selected adult subjects had a mean activity of 10.2 +/-2.4 (mean +/-S.D.) units/ml packed red blood cells. The range of activities was from 4.6 to 14.2 units/ml. The results of experiments in which partially purified human kidney TPMT was added to RBC lysates and of experiments in which "low" and "high" activity lysates were mixed gave no indication that individual variations in RBC TPMT activity were due to endogenous inhibitors or activators of the enzyme. << Less
Clin. Chim. Acta 85:323-333(1978) [PubMed] [EuropePMC]
This publication is cited by 1 other entry.