We report herein the X-ray magnetic circular dichroism (XMCD) at the Au L2,3 edges of a series of Au clusters protected by glutathione (GSH). The samples used here included AuN(SG)M with (N, M) = (10, 10), (15, 13), (18, 14), (22, 16), (25, 18), (29, 20), (39, 24) and a sodium gold(I) thiomalate (SGT) as a reference. Magnetic moments per cluster were found to be increased with size, whereas those per Au-S bond were nearly constant. This finding suggests that a localized hole created by Au-S bonding at the gold/glutathione interface, rather than the quantum size effect, is responsible for the spin polarization of gold clusters.

Humans take a long time to respond to the slow visual motion of an object. It is not known what neural mechanism causes this delay. We measured magnetoencephalographic neural responses to light spot motion onset within a wide speed range (0.4-500 degrees /sec) and compared these with human reaction times (RTs). The mean response latency was inversely related to the speed of motion up to 100 degrees /sec, whereas the amplitude increased with the speed. The response property at the speed of 500 degrees /sec was different from that at the other speeds. The speed-related latency change was observed when the motion duration was 10 msec or longer in the speed range between 5 and 500 degrees /sec, indicating that the response is directly related to the speed itself. The source of the response was estimated to be around the human MT+ and was validated by functional magnetic imaging study using the same stimuli. The results indicate that the speed of motion is encoded in the neural activity of MT+ and that it can be detected within 10 msec of motion observation. RT to the same motion onset was also inversely related to the speed of motion but the delay could not be explained by the magnetic response latency change. Instead, the reciprocal of RT was linearly related to the reciprocal of the magnetic response latency, suggesting that the visual process interacts with other neural processes for decision and motor preparation.

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Ligand-induced dimerization is a key step in the activation of receptor tyrosine kinases, including the epidermal growth factor receptor, stem cell factor receptor (c-kit),and colony-stimulating factor 1 receptor (c-fins 17) and bivalent monoclonal antibodies to the growth hormone receptor worked as agonists, whereas their monovalent fragments did not (18). These suggest that ligand-induced dimerization is also a key step in activating cytokine receptors as well as receptor tyrosine kinases.Biochemical approaches to determine the quatemary structure of the EPOR have not been very successful, mainly due to the extremely low expression level of the EPOR on the cell surface (19,20). Thus, to investigate the role of dimerization and protein phosphorylation in the action of the EPOR, we constructed hybrid receptors between the EPOR and some receptor tyrosine kinases and found that these chimeric receptors were functionally activated by the respective ligands. This study demonstrates the interchangeability of domains between two distinct receptor families and the important role of receptor dimerization in the activation of the EPOR. (22), and the mouse c-kit cDNA in the expression vector pEFneo (23) have been described. The cDNA for human c-fms (24) was provided by A. Tojo (Tokyo University). The cDNAs for chimeric receptors between the EPOR and receptor tyrosine kinases were constructed by means of the polymerase chain reaction (PCR) (25). Primers were designed to create restriction enzyme sites at the 5' and 3' ends that were used for ligation and subcloning of the PCR products. The cDNA fragments for the extracellular domain of the EGFR and the cytoplasmic domain of the EPOR were ligated into the BamHI/EcoRI sites of pSRneo-EGFR. Other constructs were subcloned into the EcoRl/Not I sites of pEFneo. The resulting chimeric cDNAs for the EGFR/EPOR and kitl EPOR encode codons -24 to 647 of the EGFR and 251-483 of the murine EPOR and encode codons -22 to 495 of c-kit, Thr-Arg at the junction, and 206-483 of the EPOR, respectively (see Fig. 1 MATERIALS AND METHODS