With short term shearing at low degrees of supercooling a method has been developed by which nucleation during shearing can effectively be separated from the subsequent crystal growth, which, in these experiments, mainly occurs after the cessation of the flow. In this way the kinetics of nucleation by shear could be unravelled for isotactic polypropylene. The required measurement consists of the monitoring of the optical retardation which increases with the monitoring time and levels off by saturation. From these measurements conclusions could be drawn with respect to the modes of formation of the nuclei and of their type. Model predictions could be confirmed with the aid of electron micrographs.

The two most prominent neutral lipids of the yeast Saccharomyces cerevisiae, triacylglycerols (TAG) and steryl esters (SE), are synthesized by the two TAG synthases Dga1p and Lro1p and the two SE synthases Are1p and Are2p. In this study, we made use of a set of triple mutants with only one of these acyltransferases active to elucidate the contribution of each single enzyme to lipid particle (LP)/droplet formation. Depending on the remaining acyltransferases, LP from triple mutants contained only TAG or SE, respectively, with specific patterns of fatty acids and sterols. Biophysical investigations, however, revealed that individual neutral lipids strongly affected the internal structure of LP. SE form several ordered shells below the surface phospholipid monolayer of LP, whereas TAG are more or less randomly packed in the center of the LP. We propose that this structural arrangement of neutral lipids in LP may be important for their physiological role especially with respect to mobilization of TAG and SE reserves.Fatty acids and sterols are important building blocks of biomembranes. To maintain balanced cellular levels of these components, a certain portion is put on hold in the form of complex neutral lipids. The yeast Saccharomyces cerevisiae similar to other eukaryotic cells stores fatty acids and sterols in the form of triacylglycerols (TAG) 3 and steryl esters (SE). Both TAG and SE are hydrophobic molecules that are not soluble in the cytosol but are also not typical bilayer membrane lipids. Consequently, they need to be stored in specific subcellular compartments that are known as lipid particles (LP), lipid droplets, lipid bodies, or oil bodies. Yeast LP are small spherical organelles with an approximate diameter of 400 nm consisting of 95% neutral lipids, TAG, and SE, and only small amounts of phospholipids and proteins (1). The highly hydrophobic core formed by TAG and SE is surrounded by a phospholipid monolayer containing a well defined set of proteins (2).Identification of LP proteins in various types of cells has changed the view of this organelle. The presence of certain enzymes on the surface of LP suggests that besides lipid storage LP are involved in various metabolic processes. In S. cerevisiae ϳ40 proteins are known to be present on the surface of LP. Strikingly, most of these proteins are enzymes involved in lipid metabolism. As prominent examples, LP from S. cerevisiae harbor enzymes of phosphatidic acid biosynthesis (3), fatty acid activation (4 -6), sterol biosynthesis (7), but also TAG biosynthesis and degradation (8 -11) and SE hydrolysis (12-14).The biogenesis of LP is still a matter of dispute and is under investigation in several laboratories. Whereas little is known about the cell biology of this process, enzymes involved in the formation of major LP components, TAG and SE, have been identified within the last few years (for recent review see Refs. 15 and 16). In the yeast as in other types of cells, the last step of TAG synthesis requires acylation of diacylglycerol. Two different ...

Disorders with Lewy body (LB) formation, such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB), are characterized by alpha-synuclein accumulation in the neuronal cell body. Recent studies have suggested that in addition to LBs, alpha-synuclein might accumulate more widely throughout the neurons and their processes, leading to neurodegeneration and functional impairment. The precise patterns of alpha-synuclein accumulation in vivo, however, and its relationship with subcellular neuronal alterations such as lysosomal pathology are not completely clear. To this end, we developed transgenic (tg) in vivo and in vitro models expressing a stable enhanced green fluorescent protein (eGFP) tagged in the C-terminal site of a human (h)alpha-synuclein construct under the regulatory control of the platelet-derived growth factor-beta (PDGFbeta) promoter and carried out confocal, ultrastructural, and biochemical studies. In tg mice, confocal studies demonstrated a wide distribution of halpha-synuclein-eGFP in the neuronal cell bodies, axons, and presynaptic terminals. In several neuronal cell bodies and their neurites, halpha-synuclein-eGFP was found not only as inclusions but also as discrete granular structures that in double-labeling studies colocalized with antibodies against halpha-synuclein and the lysosomal marker cathepsin D. Consistent with these findings, ultrastructural analysis showed that halpha-synuclein-eGFP overexpression resulted in the accumulation of electrodense inclusions and laminated bodies suggestive of lysosomal pathology, and that the halpha-synuclein-eGFP protein was more abundant in the lysosomal fractions of the tg animals. Taken together, these findings support the notion that enhanced visualization of alpha-synuclein utilizing a hybrid eGFP molecule reveals a more widespread accumulation of this molecule in several neuronal compartments, promoting lysosomal dysfunction. Furthermore, the PDGFbeta-halpha-synuclein-eGFP tg model might be a valuable tool in testing new treatments for LBD in a fast and reliable manner.