Activity-Dependent Bulk Synaptic Vesicle Endocytosis—A Fast,High Capacity Membrane Retrieval Mechanism

Central nerve terminals are placed under considerable stress during intense stimulation due to large numbers of synaptic vesicles (SVs) fusing with the plasma membrane. Classical clathrin-dependent SV endocytosis cannot correct for the large increase in nerve terminal surface area in the short term, due to its slow kinetics and low capacity. During such intense stimulation, an additional SV retrieval pathway is recruited called bulk endocytosis. Recent studies have shown that bulk endocytosis fulfils all of the physiological requirements to remedy the acute changes in nerve terminal surface area to allow the nerve terminal to continue to function. This review will summarise the recent developments in the field that characterise the physiology of bulk endocytosis which show that it is a fast, activity-dependent and high capacity mechanism that is essential for the function of central nerve terminals.     

维甲酸对人神经母细胞瘤SK—N—SH细胞形态结构和分化标志物表达的影响

目的：观察维甲酸对人神经母细胞瘤SK-N-SH细胞形态与超微结构及其相关标志物表达的影响,以鉴定其对神经母细胞瘤细胞终末分化的诱导作用。方法：1μmol／L维甲酸处理SK—N—SH细胞,光镜、电镜和免疫细胞化学检测研究SK—N—SH细胞处理前后细胞形态、超微结构变化和神经元相关标志物的表达变化。结果：光镜与电镜观察结果显示,SK—N—SH细胞经1μmol／LRA处理后,细胞形态和超微结构产生了细胞呈极性状、伸出多个轴突树突状突起、细胞逐渐变小变圆并融合在一起形成类似神经节样结构、细胞表面微绒毛减少、核仁变少变小、常染色质增多、细胞器丰富发达等显著变化;免疫细胞化学检测显示经RA处理后SK-N-SH细胞NSE、MAP2、Synaptophysin的表达较对照组细胞明显加强。结论：维甲酸能改变SK—N—SH细胞形态和超微结构恶性表型特征,并促进与神经细胞相关的终末分化指标的表达,从而对人神经母细胞瘤细胞的终末分化具有显著的诱导作用。     

The influence of PAMAM dendrimers surface groups on their interaction with porcine pepsin

In this study the ability of three polyamidoamine (PAMAM) dendrimers with different surface charge (positive, neutral and negative) to interact with a negatively charged protein (porcine pepsin) was examined. It was shown that the dendrimer with a positively charged surface (G4 PAMAM-NH₂), as well as the dendrimer with a neutral surface (G4 PAMAM-OH), were able to inhibit enzymatic activity of pepsin. It was also found that these dendrimers act as mixed partially non-competitive pepsin inhibitors. The negatively charged dendrimer (G3.5 PAMAM-COOH) was not able to inhibit the enzymatic activity of pepsin, probably due to the electrostatic repulsion between this dendrimer and the protein. No correlation between changes in enzymatic activity of pepsin and alterations in CD spectrum of the protein was observed. It indicates that the interactions between dendrimers and porcine pepsin are complex, multidirectional and not dependent only on disturbances of the secondary structure.     

Distinct Physiological Roles of Two Membrane-Bound Dehydrogenases Responsible for D-Sorbitol Oxidation in Gluconobacter frateurii

Two different membrane-bound enzymes oxidizing D-sorbitol are found in Gluconobacter frateurii THD32: pyroloquinoline quinone-dependent glycerol dehydrogenase (PQQ-GLDH) and FAD-dependent D-sorbitol dehydrogenase (FAD-SLDH). In this study, FAD-SLDH appeared to be induced by L-sorbose. A mutant defective in both enzymes grew as well as the wild-type strain did, indicating that both enzymes are dispensable for growth on D-sorbitol. The strain defective in PQQ-GLDH exhibited delayed L-sorbose production, and lower accumulation of it, corresponding to decreased oxidase activity for D-sorbitol in spite of high D-sorbitol dehydrogenase activity, was observed. In the mutant strain defective in PQQ-GLDH, oxidase activity with D-sorbitol was much more resistant to cyanide, and the H⁺/O ratio was lower than in either the wild-type strain or the mutant strain defective in FAD-SLDH. These results suggest that PQQ-GLDH connects efficiently to cytochrome bo ₃ terminal oxidase and that it plays a major role in L-sorbose production. On the other hand, FAD-SLDH linked preferably to the cyanide-insensitive terminal oxidase, CIO.