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