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PubMed2002

Maleimides stimulate oxygen reduction in illuminated thylakoids.

N-ethylmaleimide (NEM) and N,N'-(1,4-phenylene)dimaleimide (PDM) were discovered to stimulate light-induced oxygen uptake in isolated thylakoids, and PDM provided the same stimulation at one order less concentrations. Oxygen uptake rate increased promptly after NEM or PDM addition to thylakoids. The inhibitors of photosynthetic electron transport as well as catalase decreased this rate close to zero, whereas ascorbate increased it almost three-fold. Dithiothreitol suppressed oxygen uptake stimulated by NEM. NEM stimulated light-induced reduction of cytochrome c, and this stimulation was suppressed by superoxide dismutase. It was concluded that NEM and PDM being reduced can effectively reduce molecules O(2) producing superoxide radicals.

Dithiothreitol↗
PubMed1982

Quantitative determination of free thiol and disulphide groups by a fluorescent maleimide procedure.

To determine the quantitative reliability of thiol histofluorometry, the distribution of protein thiol and disulphide groups was reinvestigated in normal human epidermis, labelled with DACM-3 after cryocutting. Microscopical observations roughly confirmed, that living keratinocytes and inner stratum corneum are the main sites of free thiol groups, while disulphide crosslinks are almost exclusively found in cornified cells. Histofluorometric quantitation led to free--SH, --S--S-- or combined --SH and --S--S-profiles through the different strata, that were not compatible with previous absorption-histophotometric studies and lacked internal consistency. The difficulties reside mainly at the methodological level and may partially be resolved--at least in keratinocytes--by extraction of nonstructural SH-groups in a prerinsing step. Permanent mounting further contribute to the realization of normal fluorescence behaviour, as visualized by the decay curves. DACM-saturation of structural protein reactive groups was only reached after prolonged staining.

Disulfides↗
PubMedDate not supplied

Synthesis and biological activity of water-soluble maleimide derivatives of the anticancer drug carboplatin designed as albumin-binding prodrugs.

Four platinum (II) complexes (13-16) were synthesized by reacting either [Pt trans-DACH](NO(3))(2) with a 6-maleimidocaproic acid, a 15-maleimido-4,7,10,13-tetroxapentadecanoic acid, and a 6-maleimido-4-oxacaproic ester derivative of cyclobutane-1,1-dicarboxylic acid (CDBA) or [Pt(NH(3))(2)](NO(3))(2) with a 6-maleimido-4-oxacaproic ester derivative of CBDA. Both complexes containing the 6-maleimido-4-oxacaproic ester (15, 16) showed good water solubility (>/=8 mg/mL) and CE experiments revealed rapid binding to human serum albumin and the formation of biadducts with dGMP and dAMP. In the MaTu xenograft model in nude mice, both complexes showed an improved antitumor effect at their maximum tolerated dose (2 x 50 mg/kg carboplatin equivalents) compared to therapy with carboplatin at equimolar dose or at its optimal dose (2 x 75 mg/kg).

Animals↗
PubMed2005

Discovery of substituted maleimides as liver X receptor agonists and determination of a ligand-bound crystal structure.

Substituted 3-(phenylamino)-1H-pyrrole-2,5-diones were identified from a high throughput screen as inducers of human ATP binding cassette transporter A1 expression. Mechanism of action studies led to the identification of GSK3987 as an LXR ligand. GSK3987 recruits the steroid receptor coactivator-1 to human LXRalpha and LXRbeta with EC(50)s of 40 nM, profiles as an LXR agonist in functional assays, and activates LXR though a mechanism that is similar to first generation LXR agonists.

ATP Binding Cassette Transporter 1↗
PubMed2000

Open analogues of arcyriaflavin A. Synthesis through Diels-Alder reaction between maleimides and 1-aryl-3-tert-butyldimethylsiloxy-1, 3-butadienes.

The preparation of a range of open analogues of arcyriaflavin A is described. The synthetic approach is based on the use of perhydroisoindole-1,3,5-triones as key intermediates, which were obtained via Diels-Alder methodology using 1-aryl-3-siloxy-1, 3-butadienes as starting materials. Fischer indolization and aromatization processes afforded different methoxy-substituted arylpyrrolocarbazoles. The stereochemistry and conformation of the Diels-Alder products and the regiochemistry of the indolization reactions are supported by NMR and molecular modeling studies.

Antineoplastic Agents↗
PubMed1989

Interaction of a permeant maleimide derivative of cysteine with the erythrocyte glucose carrier. Differential labelling of an exofacial carrier thiol group and its role in the transport mechanism.

S-(Bismaleimidomethyl ether)cysteine (Cys-Mal) was synthesized as a probe for reactive thiol groups on the erythrocyte glucose carrier. Although Cys-Mal entered cells, its reaction with intracellular GSH prevented alkylation of endofacial membrane proteins, limiting its effect to the cell surface at concentrations below 5 mM. Cys-Mal irreversibly inhibited hexose transport half-maximally at 1.5 mM by decreasing the maximal rate of transport, with no effect on the affinity of substrate for the carrier. Reaction occurred with the outward-facing form of the carrier, but did not affect the ability of the carrier to change orientation. In intact cells, several exofacial proteins were labelled by [35S]Cys-Mal, including the band-4.5 glucose carrier, the labelling of which occurred on a single site sensitive to transport inhibitors. The reactive exofacial group was a thiol group, since both transport inhibition and band-4.5 labelling by Cys-Mal were abolished by the thiol-specific and impermeant compound 5,5'-dithiobis(2-nitrobenzoic acid). Selectivity for carrier labelling in cells was increased by a double differential procedure, which in turn allowed localization of the exofacial thiol group to the Mr 18,000-20,000 membrane-bound tryptic carrier fragment. In protein-depleted ghosts the exofacial thiol group was preferentially labelled at low concentrations of [35S]Cys-Mal, whereas with the reagent at 10 mM the Mr 26,000-45,000 tryptic carrier fragment was also labelled. Cys-Mal should be useful in the study of carrier thiol-group location and function.

Biological Transport↗
PubMed2006

Molecular modeling studies of surface decoration of hemoglobin by maleimide PEG.

Surface decoration of hemoglobin (Hb) with six copies of PEG-5K employing thiolation mediated PEGylation platform neutralizes the vasoaconstricive activity of acellular Hb. The molecular size homogeneity of hexaPEGylated Hb, in spite of the fact that the PEGylation is distributed at multiple sites and PEGylation at each of the sites is not quantitative, is an unusual aspect of this PEGylation reaction. We have introduced three cys residues-Cys-13 (alpha), Cys-111 (alpha), and Cys-13 (beta)-onto Hb by molecular modeling. This new mutant Hb with four reactive Cys residues has been used to build molecular models of PEGylated Hbs with two, four, six, and eight PEG-chains of different masses. The calculated loss of surface area was used to design and gain insight into the structure and the surface shielding of PEGylated Hbs. The modeling shows the adequate surface coverage of the protein hemoglobin with six copies of PEG-5K chains and also exhibits more surface coverage of the hemoglobin as compared to that afforded by two copies of PEG-20K chains.

Computer Simulation↗