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W D Horrocks

Publications and source records attributed to W D Horrocks.

44 records · Page 3Linked to original sources
PubMed1979

Time-resolved europium(III) excitation spectroscopy: a luminescence probe of metal ion binding sites.

A laser-induced luminescence technique is introduced for probing the structure and equilibria of lanthanide complexes and lanthanide ion binding to macromolecules. The method involves the excitation of the 7F0 leads to 5D0 transition between nondegenerate levels in the europium(III) ion by means of an intense pulsed dye laser source. Excitation profits obtained by scanning the laser through the transition region reveal distinct peaks characteristic of individual europium(III) ion environments. The technique may be used to characterize the species present in complex equilibria in solution or to study europium(III) binding to macromolecules. Distinct europium(III) binding sites in thermolysin with long and short excited state lifetimes are observed.

Binding Sites↗
PubMed1979

Lanthanide ion probes of structure in biology. Environmentally sensitive fine structure in laser-induced terbium(III) luminescence.

The 488 nm line of the CW argon ion laser provides a convenient visible source for the direct excitation of the emissive 5D4 state of the Tb(III) ion. Room temperature emission spectra of Tb(III) in a variety of environments have been examined under relatively high resolution. The samples studied include structurally well-characterized crystalline solids, model chelate complexes in solution and Tb(III) bound to the enzyme thermolysin and the protein parvalbumin. The fine structure in the emissions is caused by ligand field splittings of both ground and excited state J manifolds. These spectra provide signatures sensitive to the immediate coordination environment of the Tb(III) ion. Solid state/solution state structural comparisons are made. The emission fine structure reveal differences between the EF side calcium-binding sites of parvalbumin and the calcium site 1 of thermolysin.

Calcium↗
PubMed1975

Energy transfer between terbium (III) and cobalt (II) in thermolysin: a new class of metal--metal distance probes.

The visible fluorescence of terbium(III) when bound to a calcium binding site of thermolysin is greatly enhanced with an excitation maximum at 280 nm but substitution of cobalt(II) for zinc at the active site decreases the intensity by 89.5%. Treatment with N-bromosuccinimide quenches enzyme tryptophan and Tb(III) fluorescence to a similar extent and suggests the operation of tryptophan vector Tb(III) vector Co(II) energy relay system in the enzyme. Dipoledipole radiationless energy transfer between the Tb(III) donor and the Co(II) acceptor can account for this quenching. The inherent characteristics of the metal pair limits the value of the orientation factor, K2, of the Förster equation, thereby reducing uncertainties in distance measurements by energy transfer compared with other systems. A quantum yield of 0.51 yields a value of R0, the distance for 50% energy transfer, of 19.6 A, and a distance, R, between Tb(III) and Co(II) of 13.7 A, a value identical to that measured for the distance between the active site zinc atom and calcium atom number 1 by x-ray analysis in native thermolysin crystals. The limits of confidence of this measurement are discussed. Energy transfer between two different metal atom sites of a protein provides a new class of probes to measure intramolecular distances of biological macromolecules in solution.

Binding Sites↗