Electrical and Electrochemical Tests of Performance of Polographs: I. Needs and Methods; II. Diagnostic Criteria for Establishing the Degree to Which Recorded Polarograms Are Adversely Affected by Circuit Performance†

SUMMARY

Both electrical and electrochemical tests are required to define, describe, and specify the performance of a polarograph when a polarograph or a cell or an electrode is newly constructed or placed in service, when work is to be started that is of special importance, or when poor results are obtained with a combination that has been in use. In the last case, the first question is whether the malfunction originates in the polarograph itself or in the cell-electrode assembly or is due to electrochemical problems specific to the sample just introduced. The polarograph is tested by means of electrical tests. If it is performing according to specifications, the overall system (and thus the cell and electrodes) is checked out by means of obtaining polarograms with reactions of well-known characteristics. Satisfactory electrical and electrochemical test methods which have evolved at Oak Ridge National Laboratory (ORNL) are set forth in this paper. For any specific polarograph, each of these tests is generally applicable, provided, of course, that the polarograph includes the feature or mode of operation for which the test is designed. Also, diagnostic criteria are given for establishing the degree to which the forms of recorded regular, first derivative, and second derivative dc polarograms (for simple, polarographically reversible test reactions) are adversely affected by circuit performance.     

Using sequence logos and information analysis of Lrp DNA binding sites to investigate discrepanciesbetween natural selection and SELEX

In vitro experiments that characterize DNA-protein interactions by artificial selection, such as SELEX,are often performed with the assumption that the experimental conditions are equivalent to natural ones. To test whether SELEX gives natural results, we compared sequence logos composed from naturally occurring leucine-responsive regulatory protein (Lrp) binding sites with those composed from SELEX-generated binding sites. The sequence logos were significantly different, indicating that the binding conditions are disparate. A likely explanation is that the SELEX experiment selected for a dimeric or trimeric Lrp complex bound to DNA. In contrast, natural sites appear to be bound by a monomer. This discrepancy suggests that in vitro selections do not necessarily give binding site sets comparable with the natural binding sites.     

Using fluorescence-based human androgen receptor gene assay to analyze the clonality of microdissected dendritic cell tumors

The AGT1 permease is a alpha-glucoside-H+ symporter responsible for the active transport of maltose, trehalose, maltotriose, alpha-methylglucoside, melezitose and sucrose. In wild-type as well as in MAL constitutive strains, alpha-methylglucoside seemed to be the best inducer of transport activity, while trehalose had no inducing effect. Based on the initial rates of transport it seems that the sugar preferentially transported by this permease is trehalose, followed by sucrose.     

Creatine and cyclocreatine treatment of human colon adenocarcinoma xenografts: 31P and 1H magnetic resonance spectroscopic studies

Creatine (Cr) and cyclocreatine (cyCr) have been shown to inhibit the growth of a variety of human and murine tumours. The purpose of this study was to evaluate the anti-tumour effect of these molecules in relation to drug accumulation, energy metabolism, tumour water accumulation and toxicity. Nude mice carrying a human colon adenocarcinoma (LS174T) with a creatine kinase (CK) activity of 2.12 units mg(-1) protein were fed Cr (2.5% or 5%) or cyCr (0.025%, 0.1% or 0.5%) for 2 weeks and compared with controls fed standard diet. Cr concentrations of 2.5% and 5% significantly inhibited tumour growth, as did 0.1% and 0.5% cyCr. In vivo 31P magnetic resonance spectroscopy (MRS) after 2 weeks of treatment showed an increase in [phosphocreatine (PCr)+phosphocyclocreatine (PcyCr)]/nucleoside triphosphate (NTP) with increasing concentrations of dietary Cr and cyCr, without changes in absolute NTP contents. The antiproliferative effect of the substrates of CK was not related to energy deficiency but was associated with acidosis. Intratumoral substrate concentrations (measured by 1H-MRS) of 4.8 micromol g(-1) wet weight Cr (mice fed 2.5% Cr) and 6.2 micromol g(-1) cyCr (mice fed 0.1% cyCr) induced a similar decrease in growth rate, indicating that both substrates were equally potent in tumour growth inhibition. The best correlant of growth inhibition was the total Cr or (cyCr+Cr) concentrations in the tissue. In vivo, these agents did not induce excessive water accumulation and had no systemic effects on the mice (weight loss, hypoglycaemia) that may have caused growth inhibition.