Chalcopyrite-type CuInS 2 -based alloyed fluorescent nanocrystals (NCs), which contain no regulated heavy metal ions, were synthesized by heating an organometallic solution to demonstrate optical property tunability. Introduction of Zn into the CuInS 2 system enhanced their photoluminescence (PL) intensity. The resultant particles were 3-6 nm; they varied with experimental conditions and were discrete and colloidally stable. The band-gap energy and PL wavelength of Zn-Cu-In-S (ZCIS) NCs varied with Zn content and particle size. Their PL was controllable within 570-800 nm by altering the band-gap energy. Furthermore, indium substitution with gallium was shown to control band-gap energy toward ∼3.1 eV, 500 nm of PL wavelength. In addition, ZnS coating of this nanocrystal can approximately double the PL strength. Finally, surface treatment with mercaptoundecanoic acid dispersed hydrophilic ZCIS NCs into water.

1995; Nesterov et al., 1995a;Ohno et al., 1995;Heilker et al., 1996). The α chain of the AP-2 heterotetramer can Many plasma membrane proteins destined for endobind clathrin (Goodman and Keen, 1995), synaptotagmin cytosis are concentrated into clathrin-coated pits (Zhang et al., 1994), Eps15 (Benmerah et al., 1995 Tebar through the recognition of a tyrosine-based motif ), Grb2 (Okabayashi et al., 1996 and small their cytosolic domains by an adaptor (AP-2) complex.phosphorylated molecules like inositol phosphates and The μ2 subunit of isolated AP-2 complexes binds phosphoinositides (Beck and Keen, 1991a; Timerman specifically, but rather weakly, to proteins bearing et al., 1992;Voglmaier et al., 1992; Gaidarov et al., 1996). the tyrosine-based signal. We now demonstrate, usingThe physiological significance of these interactions is peptides with a photoreactive probe, that this binding under investigation. The β chain contacts clathrin and is strengthened significantly when the AP-2 complex drives coat assembly (Ahle and Ungewickell, 1989; is present in clathrin coats, indicating that there is Schroder and Ungewickell, 1991; Gallusser and cooperativity between receptor-AP-2 interactions and Shih et al., 1995). The μ2 chain coat formation. Phosphoinositides with a phosphate at recognizes the tyrosine-based endocytic motif (Ohno et al., the D-3 position of the inositol ring, but not other 1995; Boll et al., 1996), a sequence of four amino isomers, also increase the affinity of the AP-2 complex acids of the form tyrosine-polar-polar-large hydrophobic for the tyrosine-based motif. AP-2 is the first protein (YppØ), which is used for sorting proteins from the plasma known (in any context) to interact with phosphatidylmembrane to the endosome (Trowbridge et al., 1993; inositol 3-phosphate. Our findings indicate that recep- Thomas and Roth, 1994). tor recruitment can be coupled to clathrin coatThe interactions just described do not by themselves assembly and suggest a mechanism for regulation of explain how cargo recruitment and coat formation are membrane traffic by lipid products of phosphoinositide coupled and how concentration of cargo into coated 3-kinases.structures is achieved. Previous work has shown that the Keywords: adaptors/clathrin/coated pits/membrane isolated AP-2 complex, or even its isolated μ2 subunit, traffic/protein sorting can recognize the tyrosine-based motif (Ohno et al., 1995;Boll et al., 1996). This interaction reflects the specificity seen in vivo, but it is rather weak (dissociation constant Introduction~1 0 μM). Are there regulatory mechanisms that enhance

PTB domains are non-Src homology 2 (SH2) phosphotyrosine binding domains originally described in the receptor tyrosine kinase substrate, Shc. By serial truncation, we show that a 174-residue region of Shc p52 (33-206) has full PTB activity. We also show that a 173-residue region of insulin receptor substrate-1 (IRS-1; residues 144 -316) has related PTB activity. In vitro both domains bind directly to activated insulin receptors. Binding is abrogated by substitution of Tyr-960 and selectively inhibited by phosphopeptides containing NPXY sequences. Phosphopeptide assays developed to compare PTB domain specificities show that the Shc PTB domain binds with highest affinity to ⌿XN␤ 1 ␤ 2 pY motifs derived from middle T (mT), TrkA, ErbB4, or epidermal growth factor receptors (⌿ ‫؍‬ hydrophobic, ␤ ‫؍‬ ␤-turn forming); the IRS-1 PTB domain does not bind with this motif. In contrast, both the Shc and IRS-1 PTB domains bind ⌿⌿⌿XXN␤ 1 ␤ 2 pY sequences derived from insulin and interleukin 4 receptors, although specificities vary in detail. Shc and IRS-1 are phosphorylated by distinct but overlapping sets of receptor-linked tyrosine kinases. These differences may be accounted for by the inherent specificities of their respective PTB domains.Insulin binding to the insulin receptor activates it as a substrate kinase, leading to tyrosine phosphorylation of at least two cytoplasmic proteins, IRS-1 1 and Shc (1, 2). IRS-1 is phosphorylated at many tyrosine positions (3), whereas Shc is phosphorylated predominantly at one site in cells (4). Since SH2 domain proteins bind specifically with phosphotyrosyl sites in proteins (5, 6), IRS-1 is capable of multiple interactions with SH2 proteins, including phosphatidylinositol 3-kinase, the phosphatase SH-PTP2, and Grb2, a linker protein upstream of Ras. In contrast, when Shc is phosphorylated in cells, it interacts primarily with Grb2 (7).The phosphotyrosine binding (PTB) domain (also called PID or SAIN domain) was recently found to provide a mechanism for protein binding with phosphotyrosyl sequences, distinct from SH2 domains (8 -11). Perhaps related to the phosphorylation of Shc by many tyrosine kinases, in addition to the insulin receptor, its PTB domain appears to interact with multiple phosphotyrosyl proteins (8 -12). The specificity of the Shc PTB domain can be analyzed by methods analogous to those used previously for SH2 domains. The Shc PTB domain binds with ␤ turn-forming motifs frequently containing phosphorylated NPXY sequences (13-15), in contrast with SH2 domains that bind extended phosphopeptide sequences carboxyl-terminal to phosphotyrosine (pTyr) (5, 6). Since efficient IRS-1 phosphorylation in cells also depends on the phosphorylation of a ␤ turnforming NPXY motif in insulin receptors (16), IRS-1 might contain a related PTB domain (even though IRS-1 and Shc show no extended sequence homology). In yeast two-hybrid experiments, the amino-terminal Ϸ500 residues of IRS-1 direct an interaction between the insulin receptor and IRS-1 that is functionally related to Shc PTB do...

A micro-reactor was utilized for continuous and controlled CdSe nanocrystal preparation. Effects of reaction conditions on optical properties of the nanocrystals were investigated; in this current system, rapid and exact temperature control of the micro-reactor was beneficial for controlling particle diameter and reproducible preparation of particles; additional effort was made towards narrower particle-size distributions.

Biologically active proteins are useful for studying the biological functions of genes and for the development of therapeutic drugs and biomaterials in a biotechnology industry. Overexpression of recombinant proteins in bacteria, such as Escherichia coli, often results in the formation of inclusion bodies, which are protein aggregates with non-native conformations. As inclusion bodies contain relatively pure and intact proteins, protein refolding is an important process to obtain active recombinant proteins from inclusion bodies. However, conventional refolding methods, such as dialysis and dilution, are time consuming and, often, recovered yields of active proteins are low, and a trial-and-error process is required to achieve success. Recently, several approaches have been reported to refold these aggregated proteins into an active form. The strategies largely aim at reducing protein aggregation during the refolding procedure. This review focuses on protein refolding techniques using chemical additives and laminar flow in microfluidic chips for the efficient recovery of active proteins from inclusion bodies.

We present the NMR structure of the PTB domain of insulin receptor substrate-1 (IRS-1) complexed to a tyrosine-phosphorylated peptide derived from the IL-4 receptor. Despite the lack of sequence homology and different binding specificity, the overall fold of the protein is similar to that of the Shc PTB domain and closely resembles that of PH domains. However, the PTB domain of IRS-1 is smaller than that of Shc (110 versus 170 residues) and binds to phosphopeptides in a distinct manner. We explain the phosphopeptide binding specificity based on the structure of the complex and results of site-directed mutagenesis experiments.

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Microreaction technology, which is an interdisciplinary science and engineering area, has been the focus of different fields of research in the past few years. Several microreactors have been developed. Enzymes are a type of catalyst, which are useful in the production of substance in an environmentally friendly way, and they also have high potential for analytical applications. However, not many enzymatic processes have been commercialized, because of problems in stability of the enzymes, cost, and efficiency of the reactions. Thus, there have been demands for innovation in process engineering, particularly for enzymatic reactions, and microreaction devices represent important tools for the development of enzyme processes. In this review, we summarize the recent advances of microchannel reaction technologies especially for enzyme immobilized microreactors. We discuss the manufacturing process of microreaction devices and the advantages of microreactors compared to conventional reaction devices. Fundamental techniques for enzyme immobilized microreactors and important applications of this multidisciplinary technology are also included in our topics.