Catalog No.S7129

PYR-41 is the first cell-permeable inhibitor of ubiquitin-activating enzyme E1, with no activity at E2.

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PYR-41 Chemical Structure

PYR-41 Chemical Structure
Molecular Weight: 371.3

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Product Information

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Product Description

Biological Activity

Description PYR-41 is the first cell-permeable inhibitor of ubiquitin-activating enzyme E1, with no activity at E2.
Targets Ubiquitin-activating Enzyme E1 [1]
(Cell-free assay)
IC50 <10 μM
In vitro PYR-41 (50 μM) inhibits activity of ubiquitin-activating enzyme E1 by over 90%. PYR-41 could be a target for nucleophilic attack and potentially reacts with the active site cysteine of E1. PYR-41 efficiently blocks cyclin E degradation. PYR-41 decreases the level of E1fUb thioesters in cells with a IC50 of between 10 and 25 μM, and prevents proteasome inhibitor–induced accumulation of ubiquitylated proteins. PYR-41 increases total sumoylation in cells and in cell harboring temperature-sensitive E1. PYR-41 is able to inhibit both proteasome-dependent and proteasome-independent activities of ubiquitylation. PYR-41 (50 μM) attenuates 1 ng/mL IL-1α-mediated nuclear factor-κB activation by >60% through preventing the downstream ubiquitylation and proteasomal degradation of IκBα. PYR-41 inhibits degradation of p53 and activates the transcriptional activity of p53, which enable its differentially killing transformed p53-expressing cells. [1] PYR-41 blocks ubiquitination reactions but paradoxically leads to the accumulation of high MW ubiquitinated proteins. PYR-41 also has equal or greater inhibitory activity against several deubiquitinases (DUBs) in intact cells and purified USP5 in vitro. PYR-41 also mediates cross-linking of specific protein kinases (Bcr-Abl, Jak2) to inhibit their signaling activity. [1]
In vivo

Protocol(Only for Reference)

Kinase Assay:


ubiquitylation reaction assay Rabbit or mouse E1 (~250 ng) is incubated with 32P-ubiquitin in 1 譺eaction buffer [50 mM Tris (pH 7.4), 0.2 mM ATP, 0.5 mM MgCl2] at room temperature for 15 min. In some experiments, the His-tagged mouse E1 is bound to TALON cobalt affinity resin before carrying out incubations and reactions. Mouse E1 and 32P-ubiquitin are added to the beads in 1 ?reactionbuffer and incubated as for E1 reactions. Samples are heated in nonreducing SDS-PAGE sample buffer and resolved by SDS-PAGE. Thioesters with ubiquitin are visualized by Storm PhosphoImager.

Conversion of different model animals based on BSA (Value based on data from FDA Draft Guidelines)

SpeciesMouseRatRabbitGuinea pigHamsterDog
Weight (kg)
Body Surface Area (m2)0.0070.0250.
Km factor36128520
Animal A (mg/kg) = Animal B (mg/kg) multiplied by  Animal B Km
Animal A Km

For example, to modify the dose of resveratrol used for a mouse (22.4 mg/kg) to a dose based on the BSA for a rat, multiply 22.4 mg/kg by the Km factor for a mouse and then divide by the Km factor for a rat. This calculation results in a rat equivalent dose for resveratrol of 11.2 mg/kg.

Rat dose (mg/kg) = mouse dose (22.4 mg/kg) ×  mouse Km(3)  = 11.2 mg/kg
rat Km(6)


[1] Yang Y, et al. Cancer Res, 2007, 67(19), 9472-9481.

[2] Kapuria V, et al. Biochem Pharmacol, 2011, 82(4), 341-349.

Chemical Information

Download PYR-41 SDF
Molecular Weight (MW) 371.3


CAS No. 418805-02-4
Storage 3 years -20℃powder
2 years -80℃in solvent
Synonyms N/A
Solubility (25°C) * In vitro DMSO 74 mg/mL (199.29 mM)
Water <1 mg/mL
Ethanol <1 mg/mL
In vivo 2% DMSO+30% PEG 300+5% Tween 80+ddH2O 2mg/mL
* <1 mg/ml means slightly soluble or insoluble.
* Please note that Selleck tests the solubility of all compounds in-house, and the actual solubility may differ slightly from published values. This is normal and is due to slight batch-to-batch variations.
Chemical Name Benzoic acid, 4-[4-[(5-nitro-2-furanyl)methylene]-3,5-dioxo-1-pyrazolidinyl]-, ethyl ester

Tech Support

Answers to questions you may have can be found in the inhibitor handling instructions. Topics include how to prepare stock solutions, how to store inhibitors, and issues that need special attention for cell-based assays and animal experiments.

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