In vivo quantification of citrate concentration and water T2 relaxation time of the pathologic prostate gland using H MRS and MRI

We have previously reported a striking correlation between water T₂ relaxation time and citrate concentration in the normal prostate (Liney G.P.; Lowry M.; Turnbull L.W.; Manton D.J.; Knowles A.J.; Blackband S.J.; Horsman A. Proton MR T₂ maps correlate with the citrate concentration in the prostate. NMR Biomed. 9:59–64; 1996). In this study we present data from similar studies of the pathologic gland. The findings support the hypothesis that measurement of both citrate concentration and water T₂ relaxation time in vivo may aid the differentiation of prostatic carcinoma from benign disease and normal tissue.     

Longitudinal study of iodine in toenails following IV administration of an iodine-containing contrast agent

The literature on the relationship between diet and thyroid cancer (TC) risk and the higher incidence of TC among Asian immigrants to the US compared to second and third generation subgroups has prompted epidemiologists to hypothesize that increased levels of iodine consumption may be associated with TC risk, particularly among persons with a history of clinical or subclinical thyroid dysfunction. At the University of Missouri Research Reactor (MURR), we have applied epiboron neutron activation analysis to investigate human nails as a dietary monitor for iodine. Preliminary studies have indicated a positive correlation between dietary iodine intake and the concentration of iodine in toenails. However, these studies are confounded by high iodine levels (up to 30 ppm) in approximately 5% of the nails studied. We hypothesize that, in the subjects we have studied, the high iodine levels may be due to iodine-containing medications, in particular contrast-agents containing iopamidol. This paper will report on longitudinal studies using contrast agent subjects who were followed-up for almost two years compared to a longitudinal control and a population mean. Based on this study, we suggest that iodine-containing contrast agents contaminate nail samples via non-specific binding in the short term followed by incorporation in the nail as a result of absorption.     

Matrix multiplication is determined by orthogonality and trace

Any associative bilinear multiplication on the set of n-by-n matrices over some field of characteristic not two, that makes the same vectors orthogonal and has the same trace as ordinary matrix multiplication, must be ordinary matrix multiplication or its opposite.     

Focusing mutations into the P. fluorescens esterase binding site increases enantioselectivity more effectively than distant mutations

Rational design of enzymes with improved properties, such as enantioselectivity, usually focuses mutations within the substrate binding site. On the other hand, directed evolution of enzymes usually targets the entire protein and discovers beneficial mutations far from the substrate binding site. In this paper, we propose an explanation for this discrepancy and show that a combined approach--random mutagenesis within the substrate binding site--is better. To increase the enantioselectivity (E) of a Pseudomonas fluorescens esterase (PFE) toward methyl 3-bromo-2-methylpropionate, we focused mutagenesis into the substrate binding site at Trp28, Val121, Phe198, and Val225. Five of the catalytically active mutants (13%) showed better enantioselectivity than wild-type PFE. The increases in enantioselectivity were higher (up to 5-fold, reaching E = 61) than with mutants identified by random mutagenesis of the entire enzyme.     

Effect of viscous dissipation on the mixed convection heat transfer from an exponentially stretching surface

The mixed convection flow and heat transfer from an exponentially stretching vertical surface in a quiescent fluid is analyzed using similarity solution technique. Wall temperature and stretching velocity are assumed to have specific exponential function forms. The influence of buoyancy along with viscous dissipation on the convective transport in the boundary layer region is analyzed in both aiding and opposing flow situations. The flow is governed by the mixed convection parameter Gr/Re². The velocity and temperature inside the boundary layer are observed to be influenced by the parameters like Prandtl number Pr, Gebhart number Gb. Significant changes are observed in non-dimensional skin friction and heat transfer coefficients due to viscous dissipation in the medium. The flow and temperature distributions inside the boundary layer are analyzed and the results for non-dimensional skin friction and heat transfer coefficients are discussed through computer generated plots.     

Method for determining intracapillary solution temperatures: application to sample zone heating for enhanced fluorescent labeling of proteins

A fundamental premise in CE relies heavily on the assumption that temperature within the capillary is accurately known and controlled. Theoretical calculations for sample zone and BGE temperature during voltage application are presented. We propose that transient elevation of the sample zone temperature allowed for denaturing and renaturing of proteins in the presence of a fluorescent dynamic labeling reagent. Comparison with the extent of labeling possible with standard on-column dynamic labeling in the absence of elevated temperatures showed order-of-magnitude increases in the fluorescence detection sensitivity of proteins with low surface hydrophobicity. As a result, this represents an example where excess heating in the sample zone during electrophoresis can be exploited advantageously.     

Spectroscopic studies of the anaerobic enzyme-substrate complex of catechol 1,2-dioxygenase

The basis of the respective regiospecificities of intradiol and extradiol dioxygenase is poorly understood and may be linked to the protonation state of the bidentate-bound catechol in the enzyme/substrate complex. Previous ultraviolet resonance Raman (UVRR) and UV-visible (UV-vis) difference spectroscopic studies demonstrated that, in extradiol dioxygenases, the catechol is bound to the Fe(II) as a monoanion. In this study, we use the same approaches to demonstrate that, in catechol 1,2-dioxygenase (C12O), an intradiol enzyme, the catechol binds to the Fe(III) as a dianion. Specifically, features at 290 nm and 1550 cm(-1) in the UV-vis and UVRR difference spectra, respectively, are assigned to dianionic catechol based on spectra of the model compound, ferric tris(catecholate). The UVRR spectroscopic band assignments are corroborated by density functional theory (DFT) calculations. In addition, negative features at 240 nm in UV-vis difference spectra and at 1600, 1210, and 1175 cm(-1) in UVRR difference spectra match those of a tyrosinate model compound, consistent with protonation of the axial tyrosinate ligand when it is displaced from the ferric ion coordination sphere upon substrate binding. The DFT calculations ascribe the asymmetry of the bound dianionic substrate to the trans donor effect of an equatorially ligated tyrosinate ligand. In addition, the computations suggest that trans donation from the tyrosinate ligand may facilitate charge transfer from the substrate to yield the iron-bound semiquinone transition state, which is capable of reacting with dioxygen. In illustrating the importance of ligand trans effects in a biological system, the current study demonstrates the power of combining difference UVRR and optical spectroscopies to probe metal ligation in solution.     

The study of human nails as an intake monitor for arsenic using neutron activation analysis

Arsenic is toxic to humans with the lethal dose being approximately 1 mg/kg/day. At much lower long-term exposures, arsenic is hypothesized to increase the risk of certain cancers. We have developed an irradiation position for the neutron activation analysis (NAA) of nail specimens for arsenic, in support of a case-control study involving New Hampshire residents consuming well water above the EPA Safe Drinking Water Standard of 0.050 ppm. Arsenic is bound to nail keratin through sulfhydryl groups proportional to intake providing a convenient means of integrating arsenic intake in population-based studies. Our objective was to develop the necessary facilities and procedures by which relatively small samples (i.e. 20 to 100 mg) could be accurately analyzed for arsenic, so that affordable nutritional epidemiology investigations, requiring large numbers of samples (>1000 in this case), could be undertaken. A high-flux reflector position, with minimal axial variation throughout the fuel cycle, suitable for pneumatic-tube irradiations, was characterized by measurement of the neutron flux distribution (thermal and epithermal) within the irradiation capsule over time. Results from application of the method to a case-control study of basal and squamous cell skin cancer will be presented.