Simultaneous true, gated, and coupled electron-transfer reactions and energetics of protein rearrangement.

Cytochromes c(6) and f react by three et mechanisms under similar conditions. We report temperature and viscosity effects on the protein docking and kinetics of (3)Zncyt c(6)+cyt f(III)→Zncyt c(6)(+)+cyt f(II). At 0.

Metal complexes as artificial proteases in proteomics: a palladium(II) complex cleaves various proteins in solutions containing detergents.

Most popular agents for site-specific protein cleavage are proteolytic enzymes. Because they become denatured and inactivated by detergents, enzymes are inconvenient for proteomic analysis of hydrophobic proteins which require detergents as solubilizing agents. We used cis-[Pd(en)(H(2)O)(2)](2+) (in which en represents ethylenediamine) as an artificial protease to effect cleavage of three bovine proteins, namely ubiquitin, β-casein, and serum albumin, in separate experiments.

Thioether complexes of palladium(II) and platinum(II) as artificial peptidases. residue-selective peptide cleavage by a palladium(II) complex.

We report the synthesis and characterization of perchlorate salts containing the following three novel complex cations each with a bidentate thioether ligand: binuclear cis-[Pt(CH3SCH2CH2CH2SCH3)(mu-OH)]22+, mononuclear cis-[Pt(CH3SCH2CH2CH2SCH3)(H2O)2]2+, and mononuclear cis-[Pd(CH3SCH2CH2CH2SCH3)(H2O)2]2+. Despite their analogous compositions, the mononuclear Pt(II) and Pd(II) complexes differ in the selectivity with which they promote the hydrolysis of polypeptides. The complex cis-[Pt(CH3SCH2CH2CH2SCH3)(H2O)2]2+ promotes slow but selective cleavage of Met-Pro peptide bonds at pH 2.

Platinum(II) complex as an artificial peptidase: selective cleavage of peptides and a protein by cis-[Pt(en)(H2O)2]2+ ion under ultraviolet and microwave irradiation.

Two synthetic peptides were completely cleaved by the cis-[Pt(en)(H2O)2]2+ (en is ethylenediamine) complex at pH 2.5 under thermal heating at 60 degrees C in a selective way: only the amide bonds involving the carboxylic group of the methionine residue, i.e.

Conjugate of palladium(II) complex and beta-cyclodextrin acts as a biomimetic peptidase.

We combined the newly discovered ability of [Pd(H2O)4]2+ to residue-selectively hydrolyze X-Pro bonds in peptides at 6 View Article and Find Full Text PDF

Transition-metal complexes as enzyme-like reagents for protein cleavage: complex cis-[Pt(en)(H2O)2]2+ as a new methionine-specific protease.

Complex cis-[Pt(en)(H(2)O)(2)](2+) promotes selective hydrolytic cleavage of two proteins, horse cytochrome c and bovine beta-casein. The cleavage is completed in 24 h under relatively mild conditions, at about pH 2.5, and a temperature as low as 40 degrees C.

Metalloprotein association, self-association, and dynamics governed by hydrophobic interactions: simultaneous occurrence of gated and true electron-transfer reactions between cytochrome f and cytochrome c(6) from Chlamydomonas reinhardtii.

Noninvasive reconstitution of the heme in cytochrome c(6) with zinc(II) ions allowed us to study the photoinduced electron-transfer reaction (3)Zncyt c(6) + cyt f(III) --> Zncyt c(6)(+) + cyt f(II) between physiological partners cytochrome c(6) and cytochrome f, both from Chlamydomonas reinhardtii. The reaction kinetics was analyzed in terms of protein docking and electron transfer. In contrast to various protein pairs studied before, both the unimolecular and the bimolecular reactions of this oxidative quenching take place at all ionic strengths from 2.

Combined use of platinum(II) complexes and palladium(II) complexes for selective cleavage of peptides and proteins.

This study shows, for the first time, the advantages of combining two transition-metal complexes as selective proteolytic reagents. In this procedure, cis-[Pt(en)(H(2)O)(2)](2+) is followed by [Pd(H(2)O)(4)](2+). In the peptide AcAla-Lys-Tyr-Gly-Gly-Met-Ala-Ala-Arg-Ala, the Pt(II) reagent cleaves the Met6-Ala7 peptide bond, whereas the Pd(II) reagent cleaves the Gly4-Gly5 bond.

Effects of the environment on microperoxidase-11 and on its catalytic activity in oxidation of organic sulfides to sulfoxides.

Microperoxidase-11 (MP-11, also known as heme undecapeptide of cytochrome c) was immobilized by encapsulation into sol-gel silica glass and by physisorption, chemisorption, and covalent attachment to silica gel. We then compared these species with one another and with dissolved microperoxidase-11 as catalysts for the sulfoxidation of methyl phenyl sulfide by hydrogen peroxide. MP-11 is prone to oligomerization in solution, both via axial ligation and via intermolecular interactions.

Palladium(II) complex as a sequence-specific peptidase: hydrolytic cleavage under mild conditions of X-Pro peptide bonds in X-Pro-Met and X-Pro-His segments.

The X-Pro peptide bond (in which X represents any amino acid residue) in peptides and proteins is resistant to cleavage by most proteolytic enzymes. We show that [Pd(H(2)O)(4)](2+) ion can selectively hydrolyze this tertiary peptide bond within the X-Pro-Met and X-Pro-His sequence segments. The hydrolysis requires an equimolar amount of the Pd(II) reagent and occurs under mild conditions-at temperature as low as 20 degrees C (with half-life of 1.

Interplay of terminal amino group and coordinating side chains in directing regioselective cleavage of natural peptides and proteins with palladium(II) complexes.

Palladium(II) ions anchored to side chains of histidine and methionine residues in peptides and proteins in weakly acidic aqueous solutions promote hydrolytic cleavage of proximate amide bonds in the backbone. In this study, we determine how attachment of Pd(II) ions to histidine and methionine anchors and also to the terminal amino group in six natural peptides (chains A and B of insulin, segment 11-14 of angiotensinogen, pentagastrin, angiotensin II, and segment 3-8 of angiotensin II) and two proteins (ubiquitin and cytochrome c) affects regioselectivity and rate of backbone cleavage. These Pd(II)-promoted reactions follow a clear pattern of regioselectivity, directed by the anchoring side chains.

Mimicking biological electron transport in sol-gel glass: photoinduced electron transfer from zinc cytochrome C to plastocyanin or cytochrome C mediated by mobile inorganic complexes.

Biomimetic studies of electron-transport chains are important for establishing the molecular mechanisms of long-range communications between proteins. We mimic these biological assemblies by encapsulating metalloproteins in sol-gel silica glass and letting mobile inorganic complexes shuttle electrons between the immobilized proteins. We present two examples of such rudimentary electron-transport chains.

Molten-globule and other conformational forms of zinc cytochrome C. Effect of partial and complete unfolding of the protein on its electron-transfer reactivity.

To test the effect of protein conformation on reactivity, we use laser flash photolysis to compare the electron-transfer properties of the triplet state of zinc-substituted cytochrome c, designated (3)Zncyt, in the folded forms at low (F(low)) and high (F(high)) ionic strength, molten-globule (MG) form, and the forms unfolded by acid (U(acid)) and urea (U(urea)) toward the following four oxidative quenchers: Fe(CN)(6)(3-), Co(acac)(3), Co(phen)(3)(3+), and iron(III) cytochrome c. We characterize the conformational forms of Zncyt on the basis of the far-UV circular dichroism, Soret absorption, and rate constant for natural decay of the triplet state. This rate constant in the absence of quencher increases in the order F(high) < F(low) < MG < U(acid) < U(urea) because the exposure of porphyrin to solvent increases as Zncyt unfolds.

Palladium(II) complexes, as synthetic peptidases, regioselectively cleave the second peptide bond "upstream" from methionine and histidine side chains.

Palladium(II) complexes promote hydrolysis of natural and synthetic oligopeptides with unprecedented regioselectivity; the only cleavage site is the second peptide bond upstream from a methionine or a histidine side chain, that is, the bond involving the amino group of the residue that precedes this side chain. We investigate this regioselectivity with four N-acetylated peptides as substrates: neurotransmitter methionine enkephalin (Ac-Tyr-Gly-Gly-Phe-Met) and synthetic peptides termed Met-peptide (Ac-Ala-Lys-Tyr-Gly-Gly-Met-Ala-Ala-Arg-Ala), His-peptide (Ac-Val-Lys-Gly-Gly-His-Ala-Lys-Tyr-Gly-Gly-Met(OX)-Ala-Ala-Arg-Ala), in which a Met is oxidized to sulfone, and HisMet-peptide (Ac-Val-Lys-Gly-Gly-His-Ala-Lys-Tyr-Gly-Gly-Met-Ala-Ala-Arg-Ala). While maintaining protein-like properties, these substrates are suitable for quantitative study since their coordination to Pd(II) ion can be determined (by NMR spectroscopy), and the cleavage fragments can be separated (by HPLC methods) and identified (by MALDI mass spectrometry).

The binary adduct of 3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]triaconta-11,13,24,26(1),27,29-hexaene and benzene-1,2,4,5-tetracarboxylic acid.

The crystals of the title salt, 6,21-diaza-3,9,18,24-tetraazoniatricyclo[22.2.2.

Alcoholysis of Urea Catalyzed by Palladium(II) Complexes.

The palladium(II) aqua complex cis-[Pd(en)(H(2)O)(2)](2+) catalyzes the alcoholysis of urea into alkyl carbamate and ammonia. The observed rate constants for the ester formation fall in the range from 1.8 x 10(-)(5) to 5.

Regioselective Cleavage by a Palladium(II) Aqua Complex of a Polypeptide in Different Overall Conformations.

Two molecules of the complex cis-[Pd(en)(H(2)O)(2)](2+) lose aqua ligands and bind to His5 and His9 residues in the nonadecapeptide that is the carboxy-terminal segment of the protein myohemerythrin. The known modes of palladium(II)-histidine coordination are detected by (1)H NMR spectroscopy. Only the [Pd(en)(H(2)O)](2+)group bound to His5 cleaves the polypeptide backbone; the group bound to His9 does not.

Kinetics and Mechanism of Urea Hydrolysis Catalyzed by Palladium(II) Complexes.

Four palladium(II) aqua complexes catalyze hydrolytic decomposition of urea into carbon dioxide and ammonia. The initial rates of carbon dioxide formation at 313 K and pH 3.3 fall in the range 6.