Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.1.7 (acetylcholinesterase)
 28,390 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The anticancer drug caracemide, N-acetyl-N,O- di(methylcarbamoyl)hydroxylamine, and one of its degradation products, N-acetyl-O-methylcarbamoyl-hydroxylamine, were found to inhibit the enzyme ribonucleotide reductase of Escherichia coli by specific interaction with its larger component protein R1. No effect on the smaller protein R2 was observed. The effect of the degradation product was about 30 times lower than that of caracemide itself. The caracemide inactivation of R1 is irreversible, with an apparent second-order rate constant of 150 M-1 s-1. The R1R2 holoenzyme was approximately 30 times more sensitive to caracemide inactivation than the isolated R1 protein. The ribonucleotide reductase substrates were potent competitors of the caracemide inhibition, with a Kdiss for GDP binding to R1 of 80 microM. The reducing agent dithiothreitol was also found to be a potent competitor of caracemide inactivation. These results indicate that caracemide inactivates R1 by covalent modification at the substrate-binding site. By analogy with the known interaction between caracemide and acetylcholinesterase or choline acetyltransferase, we propose that the modification of R1 occurs at an activated cysteine or serine residue in the active site of the enzyme.
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PMID:Caracemide, a site-specific irreversible inhibitor of protein R1 of Escherichia coli ribonucleotide reductase. 161 68

Preclinical pharmacologic studies of caracemide [N-acetyl-N-(methylcarbamoyloxy)-N'-methylurea; CAR] have demonstrated a marked instability of this compound in the presence of either phosphate buffer (pH 7.4) or human plasma. Using [1-14C-acetyl]CAR and [3H-methylcarbamoyloxy]CAR, three CAR degradation products were identified: product A, N-(methylcarbamoyloxy)acetamide; product B: N-(methylcarbamoyloxy)-N'-methylurea; and product C: N-hydroxy-N'-methylurea. CAR degradation in human plasma was demonstrated by high-performance liquid chromatography (HPLC) to occur in a time- and temperature-dependent manner. A 30-min incubation (37 degrees) of CAR (10(-4) M) with human plasma resulted in degradation of more than 55% of parent compound; at 1 hr, more than 75% of original CAR was degraded. Incubation of [1-14C-acetyl]CAR with rat brain homogenate resulted in the formation of 14CO2. This reaction was partially inhibited by coincubation with physostigmine (10(-3) M). CAR inhibited acetylcholinesterase activity in neuroblastoma cells with an IC50 of 14 microM. In mechanism of action studies, CAR was found to inhibit ribonucleotide reductase activity but only at nine times the IC50 of hydroxyurea. In contrast to hydroxyurea, CAR was found to be non-cell-cycle phase-specific and non-cross-resistant with two CHO cell lines resistant to hydroxyurea. These data demonstrate the instability of CAR; moreover, they suggest that its mechanism of cytotoxicity is distinctly different from that of hydroxyurea and that the neurotoxicity associated with CAR administration may be caused in part by inhibition of acetylcholinesterase activity.
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PMID:Biochemical pharmacology of N-acetyl-N-(methylcarbamoyloxy)-N'-methylurea (caracemide; NSC-253272). 352 74