Time-resolved study of the lowest optically accessible ion-pair state of IBr using synchrotron radiation

I will give an overview of synchrotron radiation (SR) in macromolecular crystallography (MX) instrumentation, methods and applications from the early days to the present, including the evolution of SR sources and on to the `ultimate storage ring'. The build of dedicated beamlines for resonant anomalous scattering, large unit cells, ever smaller crystals and studies up to ultra-high resolution are core benefits. Results include a high output of PDB depositions, the successful use of microcrystals, pushing the frontiers of using high and low photon energies and time-resolved structural studies at even sub-nanosecond resolutions. These intensively physics based developments will be complemented by biological and chemical crystallography research results, encompassing catalysis and marine coloration, as well as the public understanding of our science and its impacts. Spin off benefits include services to the pharmaceutical industry and helping develop chemical crystallography uses of SR. The development of the Laue method with SR has led to pioneering spin off developments in neutron MX, including transfer of the well validated Daresbury Laue software to various neutron facilities worldwide. Neutron MX is gathering pace as new instrumentation and dedicated sample preparation facilities are in place at reactor and spallation neutron sources; smaller samples and much larger molecular weight protein complexes are now feasible for investigation so as to establish their protonation states and bound water structure. With the X-ray lasers, closely linked to the SR developments, we anticipate the use of ever smaller samples such as nanocrystals, nanoclusters and single molecules, as well as opening up femtosecond time-resolved diffraction structural studies. At the SR sources, a very high throughput assessment for the best crystal samples and tackling sub-micron crystals will become widespread.

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X-ray reflectivity with a twist: Quantitative time-resolved X-ray reflectivity using monochromatic synchrotron radiation

Applied Physics Letters ◽

10.1063/1.5085063 ◽

2019 ◽

Vol 114 (8) ◽

pp. 081904 ◽

Cited By ~ 1

Author(s):

Howie Joress ◽

Shane Q. Arlington ◽

Timothy P. Weihs ◽

Joel D. Brock ◽

Arthur R. Woll

Keyword(s):

Synchrotron Radiation ◽

Time Resolved ◽

X Ray ◽

Monochromatic Synchrotron

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Multichannel FPGA-Based Data-Acquisition-System for Time-Resolved Synchrotron Radiation Experiments

IEEE Transactions on Nuclear Science ◽

10.1109/tns.2017.2655366 ◽

2017 ◽

Vol 64 (6) ◽

pp. 1320-1326 ◽

Cited By ~ 15

Author(s):

Hyeokmin Choe ◽

Semen Gorfman ◽

Stefan Heidbrink ◽

Ullrich Pietsch ◽

Marco Vogt ◽

...

Keyword(s):

Synchrotron Radiation ◽

Data Acquisition ◽

Data Acquisition System ◽

Acquisition System ◽

Time Resolved

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Ionization characteristics of the Cys-25/His-159 interactive system and of the modulatory group of papain: resolution of ambiguity by electronic perturbation of the quasi-2-mercaptopyridine leaving group in a new pyrimidyl disulphide reactivity probe

Biochemical Journal ◽

10.1042/bj2900289 ◽

1993 ◽

Vol 290 (1) ◽

pp. 289-296 ◽

Cited By ~ 22

Author(s):

G W Mellor ◽

E W Thomas ◽

C M Topham ◽

K Brocklehurst

Keyword(s):

Ph Dependence ◽

Order Rate Constant ◽

Ion Pair ◽

Catalytic Site ◽

Alkaline Media ◽

Interactive System ◽

Data Set ◽

Pka Value ◽

Compound Ii ◽

Pair State

1. A new thiol-specific reactivity probe 4,4′-dipyrimidyl disulphide [compound (VII), m.p. 110 degrees C, pKa of its monohydronated form 0.91] was synthesized and used to resolve the ambiguity of interpretation of the behaviour of papain (EC 3.4.22.2) in alkaline media known to depend to varying extents on two ionizations with pKa values approx. 8.0-8.5 and > or = 9.5 respectively. 2. A new extensive pH-second-order rate constant (k) data set for the reaction of papain with 2-(acetamido)-ethyl 2′-pyridyl disulphide (IV) demonstrated the existence of a striking rate maximum at pH approx. 4, the independence of k around pH 8 and the increase in k with increase in pH across a pKa value of 10.0, behaviour similar to that of other 2-pyridyl disulphides (R-S-S-2-Py) that lack key substrate-like binding sites in R. 3. Although the simplest interpretation of the pKa value of 10.0 assigns it to the formation of (Cys-25)-S-/(His-159)-Im from the ion-pair state of the papain catalytic site, another interpretation may be conceived in which this pKa value is assigned to another group remote from the catalytic site, the state of ionization of which modulates catalytic-site behaviour. This alternative assignment is shown to require compensating effects in the pH region around 8 such that the formation of (Cys-25)-S-/(His-159)-Im across pKa 8.0-8.5 is without net kinetic effect in the reactions of simple 2-pyridyl disulphides such as compound (IV) and 2,2′-dipyridyl disulphide (II). 4. The lower basicity of compound (VII) relative to that of compound (II) (pKa 2.45) was predicted to diminish or abolish the compensation postulated as a possibility in reactions of 2-pyridyl disulphides because of the decreased effectiveness of reaction via a (His-159)-Im+H-assisted transition state. The characteristics of the pH-dependence of the reaction of papain with compound (VII) which are quite different from those for its reaction with compound (II) support both this prediction and the alternative assignment with a value of 8.3 for the pKa of the formation of (Cys-25)-S-/(His-159)-Im. 5. Evidence that the behaviour of papain towards both substrates and some substrate-derived time-dependent inhibitors is determined not only by the loss of the (Cys-25)-S-/(His-159)-Im+H ion-pair state by dehydronation with pKa 8.3 but also by another ionization of pKa approx. 10.0 is briefly discussed.

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