No abstract available

[en] Published in summary form only

[en] Published in summary form only

No abstract available

[en] Published in summary form only

[en] The resolution function of an X-ray triple-crystal diffractometer on a rotating-anode source has been studied both experimentally and theoretically. Three different experimental configurations were used, with perfect germanium, distorted germanium and pyrolytic graphite as monochromator and analyser, leading to changes in the resolution of two orders of magnitude. The results are compared with a Gaussian description of the resolution function and it is found that this describes the width of the central part with an accuracy of better than 25%. The wings of the resolution in the high-resolution mode show the effect of the non-Gaussian resolution elements but these are reproduced by a full numerical convolution theory of the resolution function. (orig.)

No abstract available

[en] X-ray diffraction has become a powerful in situ probe of the atomic structure at the metal/electrolyte interface. Potentiodynamic measurements are discussed in which the x-ray intensity at a selected reciprocal lattice point is monitored as the applied electrode potential is cycled. This technique is termed 'x-ray voltammetry' in direct analogy to the electrochemical technique of cyclic voltammetry. The application of the technique is highlighted by examples of surface reconstruction, metal growth and the adsorption and oxidation of carbon monoxide. (author)

[en] Isolated rat pancreatic islets were pulse-labeled for 5 min with [³H]leucine then chased for 25 min, during which time endogenously labeled [³H]proinsulin becomes predominantly compartmented in immature secretory granules. The islets were then homogenized in isotonic sucrose (pH 7.4) and a beta-granule preparation obtained by differential centrifugation and discontinuous sucrose gradient ultracentrifugation. This preparation was enriched 8-fold in beta-granules. Aside from contamination with mitochondria and a limited number of lysosomes, the beta-granule preparation was essentially free of any other organelles involved in proinsulin synthesis and packaging (i.e. microsomal elements and, more particularly, Golgi complex). Conversion of endogenously labeled [³H]proinsulin was followed in this beta-granule fraction for up to 2 h at 37 degrees C in a buffer (pH 7.3) that mimicked the cationic constituents of B-cell cytosol, during which time 92% of the beta-granules remained intact. Proinsulin conversion was analyzed by high performance liquid chromatography. The rate of proinsulin conversion to insulin was stimulated by 2.2 +/- 0.1-fold (n = 6) (at a 60-min incubation) in the presence of ATP (2 mM) and an ATP regenerating system compared to beta-granule preparations incubated without ATP. This ATP stimulation was abolished in the presence of beta-granule proton pump ATPase inhibitors (tributyltin, 2.5 microM, or 1,3-dicyclohexylcarbodiimide, 50 microM). Inhibitors of mitochondrial proton pump ATPases had no effect on the ATP stimulation of proinsulin conversion. When granules were incubated in a more acidic buffer, proinsulin conversion was increased relative to that at pH 7.3. At pH 5.5, ATP no longer stimulated conversion, and tributyltin and 1,3-dicyclohexylcarbodiimide had no effect

No abstract available