Search

Low-light adapted B800 light-harvesting complex 4 (LH4) from Rhodopseudomonas palustris is a complex in which the arrangement of the bacteriochloropyll a pigments is very different from the well-known B800-850 LH2 complex. For bulk samples, the main spectroscopic feature in the near-infrared is the occurrence of a single absorption band at 802nm. Single-molecule spectroscopy can resolve the narrow bands that are associated with the exciton states of the individual complexes. The low temperature (1.2K) fluorescence excitation spectra of individual LH4 complexes are very heterogeneous and display unique features. It is shown that an exciton model can adequately reproduce the polarization behavior of the complex, the experimental distributions of the number of observed peaks per complex, and the widths of the absorption bands. The results indicate that the excited states are mainly localized on one or a few subunits of the complex and provide further evidence supporting the recently proposed structure model.

The scientific investigation of ancient paintings gives a unique insight into ancient painting techniques and their evolution through time and geographic location. This study deals with the identification of the green pigments used by one of the most important Catalan masters in Gothic times, Jaume Huguet. Other pigments and materials have also been characterized by means of conventional techniques such as optical microscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. Synchrotron radiation X‐ray diffraction has been used to produce maps of phases at a spatial resolution of 100 µm across chromatic layers.

Abstract:  Ceruloplasmin is a multi-copper oxidase, which contains most of the copper present in the plasma. It is an acute-phase reactant that exhibits a two- to three-fold increase over the normal concentration of 300 μg/ml in adult plasma. However, the precise physiological role(s) of ceruloplasmin has been the subject of intensive debate and it is likely that the enzyme has a multi-functional role, including iron oxidase activity and the oxidation of biogenic amines. The three-dimensional X-ray structure of the human enzyme was elucidated in 1996 and showed that the molecule was composed of six cupredoxin-type domains arranged in a triangular array. There are six integral copper atoms per molecule (mononuclear sites in domains 2, 4 and 6 and a trinuclear site between domains 1 and 6) and two labile sites with roughly 50% occupancy. Further structural studies on the binding of metal cations by the enzyme indicated a putative mechanism for ferroxidase activity. In this paper we report medium-resolution X-ray studies (3.0–3.5 Å) which locate the binding sites for an inhibitor (azide) and various substrates [aromatic diamines, biogenic amines and (+)-lysergic acid diethylamide, LSD]. The binding site of the azide moiety is topologically equivalent to one of the sites reported for ascorbate oxidase. However, there are two distinct binding sites for amine substrates: aromatic diamines bind on the bottom of domain 4 remote from the mononuclear copper site, whereas the biogenic amine series typified by serotonin, epinephrine and dopa bind in close vicinity to that utilised by cations in domain 6 and close to the mononuclear copper. These binding sites are discussed in terms of possible oxidative mechanisms. The binding site for LSD is also reported.

The structure of the peripheral light‐harvesting complex from Rhodopseudomonas acidophilastrain 10050 was determined by multiple isomorphous replacement methods. The derivatization of the crystals was augmented by the addition of a backsoaking stage. The soak/backsoaked data comparison had greater isomorphism and showed simpler Patterson maps than the standard native/soak comparison. Amplitudes from the derivatized then backsoaked crystals and from the derivatized crystals were compared in order to extract a subset of heavy‐atom sites. Using this information, the full array of sites were found from a derivative/native comparison, eventually leading to excellent electron‐density maps.

By using ultra-high-flux synchrotron x-radiation from a wiggler source, good Laue diffraction data have been obtained from protein microcrystals of size 30 X 35 X 10 microns3, mounted wet in glass capillaries. At the flux level of 10(13)-10(14) photons per sec/mm2, the radiation damage is still low enough to allow a large survey of reciprocal space for a microcrystal and a complete survey for a normal-sized protein crystal. The development of sources for ultra-high-intensity synchrotron radiation is thus an important improvement in the technique for determination of structure through protein crystallography as well as in other cases where crystal size is often a limiting factor.

We report here the preparation of iron-containing concanavalin A. It has a protein-to-iron ratio of 2.0, and the iron compound it contains is particulate with an average diameter of 85 A. Iron-containing concanavalin A interacts reversibly with dextran and with methyl alpha-D-glucoside. The molecular basis of these findings is discussed and a possible mechanism suggested where one of the molecular forms of concanavalin A has the structure of an apoferritin into which iron is deposited in the form of ferrihydrite.

Since its first isolation1, bovine β-lactoglobulin (BLG) has been an enigma: although it is abundant in the whey fraction of milk, its function is still not clear. The results of the many physicochemical studies on the protein need a structural interpretation. We report here the structure of the orthorhombic crystal form of cow BLG at pH 7.6, at a resolution of 2.8 Å. It has an unusual protein fold, composed of two slabs of antiparallel β-sheet, which shows a remarkable similarity to plasma retinol-binding protein. A possible binding site for retinol in BLG has been identified by model-building. This suggests a role for BLG in vitamin A transport and we have discovered specific receptors for the BLG–retinol complex in the intestine of neonate calves.