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- Lustig, Florentina, 1948, et al.
(författare)
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Alternative splicing determines the binding of platelet-derived growth factor (PDGF-AA) to glycosaminoglycans.
- 1996
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 35:37, s. 12077-85
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Tidskriftsartikel (refereegranskat)abstract
- We have shown previously that the platelet-derived growth factor (PDGF) and a synthetic oligopeptide, corresponding to the basic carboxyl-terminal amino acid extension of the long PDGF-A isoform, bind to heparin. Here, we have expressed the long (rA125) and the short (rA109) variants of PDGF A-chains in Escherichia coli and produced the functional homodimers. Surface plasmon resonance analyses showed that while the dimeric rA125 bound with high affinity to low molecular weight heparin, the rA109, lacking the basic extension, did not. This strongly indicated that high affinity binding is due to the carboxyl-terminal extension. Investigations of kinetics and thermodynamics suggested an allosteric binding mechanism. Thus, dimeric rA125 contains two equivalent binding sites. Following low affinity binding of heparin to one binding site, the dimer undergoes a conformational change, increasing the affinity for heparin about 40 times. This positive cooperativity requires the basic amino acid extension in both monomers of the dimeric PDGF molecule. Thermodynamics of the reaction, showing an entropy-driven endothermic process, suggest the involvement of hydrophobic interactions in this rearrangement. Three amino acids in the basic carboxyl-terminal extension were essential for the interaction: the basic residues Arg111 and Lys116, and the polar Thr125. We also found that other glycosaminoglycan species, corresponding to those produced by human arterial smooth muscle cells, bound to dimeric rA125 and that heparan sulfate showed the highest affinity.
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- Palacios, M.A., et al.
(författare)
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Platinum-group elements: quantification in collected exhaust fumes and studies of catalyst surfaces
- 2000
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Ingår i: The Science of the Total Environment. ; 257, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Automotive catalytic converters, in which Pt, Pd and Rh (platinum-group elements; PGEs) are the active components for eliminating several noxious components from exhaust fumes, have become the main source of environmental urban pollution by PGEs. This work reports on the catalyst morphology through changes in catalyst surface by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) and laser-induced breakdown spectrometry (LIBS) from fresh to aged catalytic converters. The distribution of these elements in the fresh catalysts analysed (PtPdRh gasoline catalyst) is not uniform and occurs mainly in a longitudinal direction. This heterogeneity seems to be greater for Pt and Pd. PGEs released by the catalysts, fresh and aged 30 000 km, were studied in parallel. Whole raw exhaust fumes from four catalysts of three different types were also examined. Two of these were gasoline catalysts (PtPdRh and PdRh) and the other two were diesel catalysts (Pt). Samples were collected following the 91441 EUDC driving cycle for light-duty vehicle testing. The results show that at 0 km the samples collected first have the highest content of particulate PGEs and although the general tendency is for the release to decrease with increasing number of samples taken, exceptions are frequent. At 30 000 km the released PGEs in gasoline and diesel catalysts decreased significantly. For fresh gasoline catalysts the mean of the total amount released was approximately 100, 250 and 50 ng km−1 for Pt, Pd and Rh, respectively. In diesel catalysts the Pt release varied in the range 400800 ng km−1. After ageing the catalysts up to 30 000 km, the gasoline catalysts released amounts of Pt between 6 and 8 ng km−1, Pd between 12 and 16 ng km−1 and Rh between 3 and 12 ng km−1. In diesel catalysts the Pt release varied in the range 108150 ng km−1. The soluble portion of PGEs in the HNO3 collector solution represented less than 5% of the total amount for fresh catalysts. For 30 000 km the total amount of soluble PGEs released was similar or slightly higher than for 0 km.
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