4-nitrophenylhydrazine and phenylhydrazine

4-n-Butylamino-5-ethyl-1,2-benzoquinone (1(ox)) has been synthesized as a model compound for the LTQ (lysine tyrosyl quinone) cofactor of lysyl oxidase (LOX). At pH 7, 1(ox) has a lambda(max) at 504 nm and exists as a neutral o-quinone in contrast to a TPQ (2,4,5-trihydroxyphenylalanine quinone) model compound, 4, which is a resonance-stabilized monoanion. Despite these structural differences 1(ox) and 4 have the same redox potential (ca. -180 mV vs SCE). The structure of the phenylhydrazine adduct of 1(ox) (2) is reported, and 2D NMR spectroscopy has been used to show that the position of nucleophilic addition is at C(1). UV-vis spectroscopic pH titration of phenylhydrazine adducts of 1(ox) and 4, 2, and 11, respectively, reveals a similar red shift in lambda(max) at alkaline pH with the same pK(a) (approximately 11.8). In contrast, the red shift in lambda(max) at acidic pH conditions yields different pK(a) values (2.12 for 2 vs -0.28 for 11), providing a means to distinguish LTQ from TPQ. Reactions between in situ generated 4-ethyl-1,2-benzoquinone and primary amines give a mixture of products, indicating that the protein environment must play an essential role in LTQ biogenesis by directing the nucleophilic addition of the epsilon-amino group of a lysine residue to the C(4) position of a putative dopaquinone intermediate. Characterization of a 1,6-adduct between an o-quinone and butylamine (3-n-butylamino-5-ethyl-1,2-benzoquinone, 13) confirms the assignment of LTQ as a 1,4-addition product.

Topics: Benzoquinones; Biomimetic Materials; Butylamines; Electrochemistry; Hydrogen-Ion Concentration; Kinetics; Lysine; Nuclear Magnetic Resonance, Biomolecular; Phenols; Phenylhydrazines; Protein-Lysine 6-Oxidase; Quinones; Spectrophotometry, Ultraviolet

An improved purification scheme for an amine oxidase from equine plasma (EPAO), a nonruminant source, is described and the protein's active-site is characterized. EPAO is dimeric and contains one Type-2 Cu(II) ion per monomer. The EPAO Cu(II) site is spectroscopically very similar to the Cu(II) sites in other amine oxidases. Unlike the extensively investigated nonruminant amine oxidase from porcine plasma, EPAO does not display half-of-the-sites reactivity; titrations with p-nitrophenylhydrazine and phenylhydrazine indicate two active cofactors per dimer. This cofactor is determined to be the same as that of other copper-containing amine oxidases, 6-hydroxydopa quinone (topa quinone). Upon anaerobic reduction with substrate at ambient temperature, the EPR spectrum of EPAO exhibits a sharp signal at g congruent to 2, attributable to the topa semiquinone. Equine plasma amine oxidase possesses novel in vitro substrate specificity; while other mammalian amine oxidases oxidize norepinephrine only slowly or not at all, EPAO displays significant activity toward this biogenic amine.

Topics: Amine Oxidase (Copper-Containing); Animals; Binding Sites; Chromatography, Affinity; Chromatography, Gel; Chromatography, Ion Exchange; Copper; Electron Spin Resonance Spectroscopy; Electrophoresis, Polyacrylamide Gel; Horses; Indicators and Reagents; Kinetics; Macromolecular Substances; Oxidoreductases Acting on CH-NH Group Donors; Phenylhydrazines; Spectrophotometry; Substrate Specificity

Interactions of two distinct quinoprotein amine oxidases from Aspergillus niger, AO-I and AO-II, with active-site covalent modifiers have been investigated. Both enzymes are inhibited similarly by phenylhydrazine or p-nitrophenylhydrazine, forming an orange Schiff base with a carbonyl group of topaquinone cofactor. Modification of histidyl and tyrosyl residues by diethylpyrocarbonate and sulfhydryl groups by 5,5'-dithio-bis-(2-nitrobenzoic acid) and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole have been described. A substrate analog, 1,4-diamino-2-butyne, was found to function as a mechanism-based inhibitor. It shows both substrate saturation kinetics and time-dependent irreversible inhibition caused by formation of pyrrole bound to the active site. The pyrrole formation was confirmed spectrophotometrically by reaction with Ehrlich's reagent at 525 nm. Inhibition by 1,4-diamino-2-butyne produces a new maximum in the absorption spectra of AO-I and AO-II at 310 nm and 306 nm, respectively. Inactivated AO-I was digested by proteases; labeled peptides were purified by C18 HPLC and sequenced by Edman degradation. Data reveal the evidence that 1,4-diamino-2-butyne reacts with the epsilon-amino group of the Lys356 residue in the sequence Lys-Met-Pro-Asn-Ala of Aspergillus niger amine oxidase AO-I.

Topics: Amine Oxidase (Copper-Containing); Amino Acid Sequence; Aspergillus niger; Binding Sites; Diamines; Diethyl Pyrocarbonate; Kinetics; Lysine; Models, Chemical; Molecular Sequence Data; Phenylhydrazines; Schiff Bases; Sequence Homology, Amino Acid; Spectrophotometry; Substrate Specificity