Exchangeable proton ENDOR as a probe of the redox-active iron center in activated bleomycin and ferric bleomycin.

Activated bleomycin (ABLM) is a drug-Fe(iii)-hydroperoxide complex kinetically competent in DNA attack (via H4' abstraction). This intermediate is relatively stable, but its spontaneous conversion to ferric bleomycin (Fe(iii)·BLM) is poorly characterized because no observable intermediate product accumulates. The Fe(iii)·BLM formed cryophotolytically from ABLM and kept at 77 K was remarkably similar by EPR and ENDOR criteria to Fe(iii)·BLM formed from Fe(iii) + BLM solution.

Pulse dipolar ESR of doubly labeled mini TAR DNA and its annealing to mini TAR RNA.

Pulse dipolar electron-spin resonance in the form of double electron electron resonance was applied to strategically placed, site-specifically attached pairs of nitroxide spin labels to monitor changes in the mini TAR DNA stem-loop structure brought on by the HIV-1 nucleocapsid protein NCp7. The biophysical structural evidence was at Ångstrom-level resolution under solution conditions not amenable to crystallography or NMR. In the absence of complementary TAR RNA, double labels located in both the upper and the lower stem of mini TAR DNA showed in the presence of NCp7 a broadened distance distribution between the points of attachment, and there was evidence for several conformers.

Porphyrin-phospholipid liposomes permeabilized by near-infrared light.

The delivery of therapeutic compounds to target tissues is a central challenge in treating disease. Externally controlled drug release systems hold potential to selectively enhance localized delivery. Here we describe liposomes doped with porphyrin-phospholipid that are permeabilized directly by near-infrared light.

The internal dynamics of mini c TAR DNA probed by electron paramagnetic resonance of nitroxide spin-labels at the lower stem, the loop, and the bulge.

Electron paramagnetic resonance (EPR) at 236.6 and 9.5 GHz probed the tumbling of nitroxide spin probes in the lower stem, in the upper loop, and near the bulge of mini c TAR DNA.

How charging corannulene with one and two electrons affects its geometry and aggregation with sodium and potassium cations.

Bowl-shaped mono- and dianions are prepared by reduction of corannulene (C(20)H(10), 1) with sodium and potassium metals in the presence of [18]crown-6 ether. Single-crystal X-ray diffraction studies of two sodium salts, [Na(THF)(2)([18]crown-6)](+)[1(-)] (2a) and [Na([18]crown-6)](+)[1(-)] (2b), reveal the presence of naked corannulene monoanions 1(-) in both cases. In contrast, the potassium adduct, [K([18]crown-6)](+)[1(-)] (3), shows an η(2)-binding of the K(+) ion to the convex face of 1(-).

Effect of freezing conditions on distances and their distributions derived from Double Electron Electron Resonance (DEER): a study of doubly-spin-labeled T4 lysozyme.

Pulsed dipolar ESR spectroscopy, DEER and DQC, require frozen samples. An important issue in the biological application of this technique is how the freezing rate and concentration of cryoprotectant could possibly affect the conformation of biomacromolecule and/or spin-label. We studied in detail the effect of these experimental variables on the distance distributions obtained by DEER from a series of doubly spin-labeled T4 lysozyme mutants.

EPR-ENDOR characterization of (17O, 1H, 2H) water in manganese catalase and its relevance to the oxygen-evolving complex of photosystem II.

The synthesis of efficient water-oxidation catalysts demands insight into the only known, naturally occurring water-oxidation catalyst, the oxygen-evolving complex (OEC) of photosystem II (PSII). Understanding the water oxidation mechanism requires knowledge of where and when substrate water binds to the OEC. Mn catalase in its Mn(III)-Mn(IV) state is a protein model of the OEC's S(2) state.

The role of arginine-127 at the proximal NO-binding site in determining the electronic structure and function of 5-coordinate NO-heme in cytochrome c' of Rhodobacter sphaeroides.

Cytochrome c' is a heme protein from a denitrifying variant of Rhodobacter sphaeroides which may serve to store and transport metabolic NO while protecting against NO toxicity. Its heme site bears resemblance through its 5-coordinate NO-binding capability to the regulatory site in soluble guanylate cyclase. A conserved arginine (Arg-127) abuts the 5-coordinate NO-heme binding site, and the alanine mutant R127A provided insight into the role of the Arg-127 in establishing the electronic structure of the heme-NO complex and in modifying the heme-centered redox potential and NO-binding affinity.

HIV-1 nucleocapsid protein NCp7 and its RNA stem loop 3 partner: rotational dynamics of spin-labeled RNA stem loop 3.

The tumbling dynamics of a 20-mer HIV-1 RNA stem loop 3 spin-labeled at the 5' position were probed in the nanosecond time range. This RNA interacted with the HIV-1 nucleocapsid Zn-finger protein, 1-55 NCp7, and specialized stopped-flow EPR revealed concomitant kinetics of probe immobilization from milliseconds to seconds. RNA stem loop 3 is highly conserved in HIV, while NCp7 is critical to HIV-RNA packaging and annealing.

Cryogenic photolysis of activated bleomycin to ferric bleomycin.

Activated bleomycin (ABLM) is a drug--Fe(III)-hydroperoxide complex kinetically competent in DNA attack (via H4' abstraction). This intermediate is relatively stable, but its spontaneous conversion to ferric bleomycin (Fe(III).BLM) is poorly characterized because no observable intermediate product accumulates.

EPR-ENDOR of the Cu(I)NO complex of nitrite reductase.

With limited reductant and nitrite under anaerobic conditions, copper-containing nitrite reductase (NiR) of Rhodobacter sphaeroides yielded endogenous NO and the Cu(I)NO derivative of NiR. (14)N- and (15)N-nitrite substrates gave rise to characteristic (14)NO and (15)NO EPR hyperfine features indicating NO involvement, and enrichment of NiR with (63)Cu isotope caused an EPR line shape change showing copper involvement. A markedly similar Cu(I)NONiR complex was made by anaerobically adding a little endogenous NO gas to reduced protein and immediately freezing.

Regulation and function of cytochrome c' in Rhodobacter sphaeroides 2.4.3.

Cytochrome c' (Cyt c') is a c-type cytochrome with a pentacoordinate heme iron. The gene encoding this protein in Rhodobacter sphaeroides 2.4.