Information processing, social cognition, and psychiatric rehabilitation in schizophrenia

Pattern electroretinograms are small physiologic signals that require good patient cooperation and long recording times, particularly when conditions are not optimal. Six electrodes were compared to evaluate their efficacy. Pattern electroretinograms were recorded in eight healthy volunteers to high-contrast, pattern-reversal checks (40' width) with Burian-Allen, DTL fiber, C-glide, gold foil, HK loop and skin electrodes. Raw data for 320 reversals were analyzed off-line to evaluate signal amplitude, quality, P50 and N95 peak times, artifact rate and electrical noise. Insertion time, impedance and subjective comfort were also assessed. The Burian-Allen contact lens electrode gave the largest signal and lowest impedance but was the least comfortable and had the highest artifact rate (p < 0.01). A skin electrode on the lower eyelid produced the smallest pattern electroretinogram with the poorest quality (p < 0.05). The four other electrodes were foil or fiber electrodes in contact with the tear film, conjunctiva and/or the inferior cornea. The signal from these showed only minor differences. When electrodes are compared for pattern electroretinograms recording, the foil and fiber electrodes do not differ substantially but contact lens and skin electrodes show substantial disadvantages.     

The binding of receptor-recognized alpha2-macroglobulin to the low density lipoprotein receptor-related protein and the alpha2M signaling receptor is decoupled by oxidation

Receptor-recognized forms of alpha2-macroglobulin (alpha2M*) bind to two classes of cellular receptors, a high affinity site comprising approximately 1500 sites/cell and a lower affinity site comprising about 60,000 sites/cell. The latter class has been identified as the so-called low density lipoprotein receptor-related protein (LRP). Ligation of receptors distinct from LRP activates cell signaling pathways. Strong circumstantial evidence suggests that the high affinity binding sites are responsible for cell signaling induced by alpha2M*. Using sodium hypochlorite, a powerful oxidant produced by the H2O2-myeloperoxidase-Cl- system, we now demonstrate that binding to the high affinity sites correlates directly with activation of the signaling cascade. Oxidation of alpha2M* using 200 microM hypochlorite completely abolishes its binding to LRP without affecting its ability to activate the macrophage signaling cascade. Scatchard analysis shows binding to a single class of high affinity sites (Kd - 71 +/- 12 pM). Surprisingly, oxidation of native alpha2-macroglobulin (alpha2M) with 125 microM hypochlorite results in the exposure of its receptor-binding site to LRP, but the ligand is unable to induce cell signaling. Scatchard analysis shows binding to a single class of lower affinity sites (Kd - 0.7 +/- 0.15 nM). Oxidation of a cloned and expressed carboxyl-terminal 20-kDa fragment of alpha2M (RBF), which is capable of binding to both LRP and the signaling receptor, results in no significant change in its binding Kd, supporting our earlier finding that the oxidation-sensitive site is predominantly outside of RBF. Attempts to understand the mechanism responsible for the selective exposure of LRP-binding sites in oxidized native alpha2M suggest that partial protein unfolding may be the most likely mechanism. These studies provide strong evidence that the high affinity sites (Kd - 71 pM) are the alpha2M* signaling receptor.     

Mapping the structural domains of E. coli carbamoyl phosphate synthetase using limited proteolysis

The structural and functional domains of Escherichia coli carbamoyl phosphate synthetase (CPS) have been identified by limited proteolysis. Incubation of CPS with several proteases, including trypsin, chymotrypsin, subtilisin and endoproteinase Asp-N, under native conditions, causes a time-dependent loss of enzymatic activity and the generation of a common fragmentation pattern. Amino-terminal sequencing studies demonstrated that the initial cleavage event by trypsin occurred at the carboxy-terminal end of the large subunit. The ultimate fragments produced in most of the proteolysis studies, 35- and 45-kDa peptides, were derived from areas corresponding to the putative ATP binding regions. Substrate protection studies showed that the addition of ligands did not affect the final fragmentation pattern of the protein. However, ornithine and UMP were found to significantly reduce the rate of inactivation by inhibition of proteolytic cleavage. MgATP and IMP provided modest protection whereas bicarbonate and glutamine showed no overall effect on proteolysis. Limited proteolysis by endoproteinase Asp-N resulted in the production of a fragment (or multiple fragments) which contained enzymatic activity but had lost all regulation by the allosteric ligands, UMP and ornithine. The small subunit has been shown to be protected from proteolysis by the large subunit. Proteolysis of the isolated small subunit resulted in the generation of a stable 31-kDa species which contained 10% of the original glutaminase activity. These studies demonstrate that a portion of the C-terminal end of the large subunit can be excised without entirely destroying the ability of CPS to catalyze the formation of carbamoyl phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chromosomal anomalies in stage D1 prostate adenocarcinoma primary tumors and lymph node metastases detected by fluorescence in situ hybridization

We previously reported a HPLC assay method using fluorimetric detection for the simultaneous determination of urinary N2-(3-aminopropyl)biopterin (oncopterin, a natural pteridine newly found in urine from cancer patients), biopterin and neopterin. We now have observed that an unknown substance, which may be derived from methotrexate, in urine from a patient with stomach cancer interfered with the assay of oncopterin and demonstrated that oncopterin could be completely separated from the unidentified substance by HPLC using a Nucleosil 100-5SA strong cation-exchange column. Furthermore, oncopterin was not detectable by this HPLC-fluorimetric method in urine samples from patients with stomach cancer who were not treated with methotrexate. The content of urinary oncopterin from cancer patients is supposed to be very low, with less than 1 mumol/mol creatinine. The present results indicate that the peak found with elution from the C18 column was a methotrexate-derived compound and co-eluted with the analyte oncopterin.