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Site-directed mutagenesis and molecular dynamics analysis of the 3-D model of the ale-adrenergic receptor (AR) were combined to identify the molecular determinants of the receptor involved in catecholamine binding. Our results indicate that the three conserved serines in the fifth transmembrane domain (TMD) of the ale-AR play a distinct role in catecholamine binding versus receptor activation. In addition to the amino acids D125 in TMDIII and S207 in TMDV directly involved in ligand binding, our findings identify a large number of polar residues playing an important role in the activation process of the CQ-AR thus providing new insights into the structure/ function relationship of G protein-coupled receptors.

In Drosophila a remarkable feature of oogenesis is the regression of the nurse cells after dumping their cytoplasmic contents into the oocyte. We have studied the nature of this process at the late stages of egg chamber development. In egg chambers DAPI staining shows highly condensed chromatin from stage 12 and TUNEL labelling shows DNA fragmentation up to stage 14. Gel electrophoresis of the end-labelled DNA, extracted from isolated egg chambers at the same stages of development, shows a ladder typical of apoptotic nuclei. This provides evidence that, during Drosophila oogenesis, the nurse cells undergo apoptosis. Apoptotic nuclei have also been detected in dumping-defective egg chambers, indicating that the cytoplasmic depletion of nurse cells is concurrent with but apparently not the cause of the process.

In Xenopus laevis eggs, cisternae shells which surround cortical granules (CG) are part of a cortical endoplasmic reticulum (ER) network. In this paper the origin of such ER shells has been studied in full-grown, progesterone-exposed Xenopus oocytes. Furthermore, the possible role of the cortical ER in the activation process has been investigated by pricking maturing oocytes. It has been shown that in full-grown ovarian oocytes ER CG shells are absent and ER cisternae are extensively and randomly distributed throughout the peripheral cytoplasm, where they appear to be continuous with annulate lamellae (AL). Following hormone treatment, the AL completely disaggregate and the ER cisternae gradually migrate to the cortex where they surround the CG constituting the typical cortical network described in uterine eggs. Furthermore, it has been found that 8 h after progesterone treatment (before the first polar body extrusion) the response to pricking (CG exocytosis) occurs only at the animal half; there is no observable response in the vegetal half. At this time ER shells surround CG only in the animal hemisphere. A complete CG exocytosis occurs following the first polar body emission, when the cortical ER is well organized in the whole oocyte cortex. The correlation between the differentiation of the cortical ER and the arousal in the oocyte of the ability to respond to a pricking stimulus is discussed in the light of an involvement of the cortical ER in the propagation of CG exocytosis.

The respiratory chain of Pseudomonas pseudoalcaligenes KF707 in membranes isolated from cells grown in the presence or absence of the toxic oxyanion tellurite (TeO Comparison of the growth curve of KF707 cells in parallel with tellurite uptake showed that intracellular accumulation of tellurium (Te 0 ) crystallites starts from the mid-exponential growth phase, whereas tellurite-induced changes of the respiratory chain are already evident during the early stages of growth. These data were interpreted as showing that reduction of tellurite to tellurium and tellurite-dependent modifications of the respiratory chain are unrelated processes in P. pseudoalcaligenes KF707.