PubMed · 4209807
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
T Bergan. 1974-06-30. [Glutaraldehyde].. https://pubmed.ncbi.nlm.nih.gov/4209807/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Proteasomes degrade endogenous proteins in the cytosol. The potential contribution of the proteasome to the effect of flanking sequences on the presentation of an antigenic epitope presented by the major histocompatibility complex class I allele Ld was studied. Peptides generated in cells from minigenes coding for peptides of 17- and 19-amino acid length were compared with the in vitro 20S proteasome degradation products of the respective synthetic peptides. The quality of generated peptides was independent of ubiquitination. In vivo and in vitro processing products were indistinguishable with respect to peptide size and abundance. Altering the neighboring sequence substantially improved the yield of the final antigenic nonapeptide by 20S proteasome cleavage. These results suggest that, in addition to the presence of major histocompatibility complex class I allelic motifs, the cleavage preference of the proteasome can define the antigenic potential of a protein.
Cis- and trans-1,4-diamino-2-butene are substrates and potent inactivators of porcine kidney diamine oxidase. Evidence from absorption and NMR spectra indicates that both are oxidized to pyrrole. Both substrates are irreversible mechanism-based inactivators of the enzyme, although the trans isomer is more potent and results in complete inactivation in a reaction which follows pseudo-first-order kinetics with an apparent Ki of 0.34 mM and a second-order inactivation constant of 500 M-1 s-1. Under the same conditions, 46% of the activity remains when the enzyme is reacted with cis-1,4-diamino-2-butene. Trans-4-amino-2-butenal, the product of oxidation of the trans diamine, has been synthesized and shown to undergo cyclization to pyrrole in a concentration-dependent manner, approaching second-order at low concentrations. Trans-4-amino-2-butenal is itself a potent irreversible inhibitor with IC50 of 2.5 microM. We propose that the irreversible inactivation by both cis- and trans-1,4-diamino-2-butene involves attack by a protein-based nucleophilic residue on the unsaturated aminoenal products of the enzymatic reactions, resulting in a covalent adduct. Cyclization of the cis-aminoenal to pyrrole is much more rapid than in the trans case, thus it is less available for inhibitory reaction with the protein.
In the present study, we investigated the mechanism(s) of ring-opening of benzene in a mouse liver microsomal system in the presence of Fe2+.HPLC analysis based on coelution with authentic standards and on-line UV spectra obtained using a diode array detector indicated that benzene is metabolized to phenol, hydroquinone (HQ), trans,trans-muconaldehyde (muconaldehyde, MUC), 6-oxo-trans,trans-2,4-hexadienoic (COOH-M-CHO), 6-hydroxy-trans,trans-2,4-hexadienal (CHO-M-OH), and 6-hydroxy-trans,trans-2,4-hexadienoic acid (COOH-M-OH). CHO-M-OH was confirmed by mass spectrometry. Muconaldehyde was also metabolized to CHO-M-OH, COOH-M-CHO and COOH-M-OH, in the same microsomal system. The inhibition of muconaldehyde metabolism by microsomes in the presence of pyrazole indicates that there is cytosolic alcohol dehydrogenase (ADH) activity in the microsomes. Metabolism by contaminating ADH of muconaldehyde formed during microsomal incubation of benzene could be involved in the formation of CHO-M-OH and COOH-M-OH. The ring-opening of benzene was stimulated by added Fe2+. Hydrogen peroxide was produced in the microsomal system and consumed in the presence of added Fe2+. Addition of catalase inhibited the formation of ring-opened products, while superoxide dismutase increased their formation in the presence of azide. Singlet oxygen scavengers, i.e. histidine, deoxyguanosine, Tris and azide (at concentrations above 1.0 mM), dramatically decreased the ring-opening of benzene. Hydroxyl radical scavengers, DMSO, mannitol and formate, but not ethanol, also decreased the ring-opening of benzene. The data indicate that Fenton chemistry plays an important role in benzene ring-opening by microsomes. An unknown peak with UV absorption maxima at 275 and 345 nm was also detected. Based on pH sensitivity of the UV spectrum, the reactivity with thiobarbituric acid (giving a chromogen with absorption maximum at 532 nm) and the molecular weight (126), this compound was identified tentatively as alpha- or beta-hydroxymuconaldehyde.