The x-ray crystal structure of phosphomannose isomerase from Candida albicans at 1.7 angstrom resolution

Phosphomannose isomerase (PMI) catalyses the reversible isomerization of fructose-6-phosphate (F6P) and mannose-6-phosphate (M6P). Absence of PMI activity in yeasts causes cell lysis and thus the enzyme is a potential target for inhibition and may be a route to antifungal drugs. The 1.7 A crystal structure of PMI from Candida albicans shows that the enzyme has three distinct domains. The active site lies in the central domain, contains a single essential zinc atom, and forms a deep, open cavity of suitable dimensions to contain M6P or F6P The central domain is flanked by a helical domain on one side and a jelly-roll like domain on the other.     

HERG-like K+ channels in microglia

A voltage-gated K+ conductance resembling that of the human ether-à-go-go-related gene product (HERG) was studied using whole-cell voltage-clamp recording, and found to be the predominant conductance at hyperpolarized potentials in a cell line (MLS-9) derived from primary cultures of rat microglia. Its behavior differed markedly from the classical inward rectifier K+ currents described previously in microglia, but closely resembled HERG currents in cardiac muscle and neuronal tissue. The HERG-like channels opened rapidly on hyperpolarization from 0 mV, and then decayed slowly into an absorbing closed state. The peak K+ conductance-voltage relation was half maximal at -59 mV with a slope factor of 18.6 mV. Availability, assessed by a hyperpolarizing test pulse from different holding potentials, was more steeply voltage dependent, and the midpoint was more positive (-14 vs. -39 mV) when determined by making the holding potential progressively more positive than more negative. The origin of this hysteresis is explored in a companion paper (Pennefather, P.S., W. Zhou, and T.E. DeCoursey. 1998. J. Gen. Physiol. 111:795-805). The pharmacological profile of the current differed from classical inward rectifier but closely resembled HERG. Block by Cs+ or Ba2+ occurred only at millimolar concentrations, La3+ blocked with Ki = approximately 40 microM, and the HERG-selective blocker, E-4031, blocked with Ki = 37 nM. Implications of the presence of HERG-like K+ channels for the ontogeny of microglia are discussed.     

Modest release of adipsin/factor D by liposuction when using the superwet or tumescent technique

Human adipsin is recognized to be identical to factor D, which plays an important role in activation of the alternative complement pathway. Since adipsin/factor D is present in high amounts in adipose tissue, liposuction theoretically could result in an increased release of this serine protease into the bloodstream. In the present study, adipsin/factor D was measured in 22 patients undergoing syringe-assisted liposuction using the superwet or tumescent technique. Despite a relatively high mean aspirate volume (2648 ml), only a very modest increase in adipsin/factor D concentration was found during liposuction. All values before, during, and after liposuction were within the range found in healthy blood donors. Furthermore, there was no correlation between adipsin/factor D values and C3 activation products. We conclude that liposuction with the present techniques results in a very modest release of adipsin/factor D that is not associated with increased complement activation.     

Macromolecular diffusion of biological polymers measured by confocal fluorescence recovery after photobleaching

Fluorescence recovery after photobleaching with an unmodified confocal laser scanning microscope (confocal FRAP) was used to determine the diffusion properties of network forming biological macromolecules such as aggrecan. The technique was validated using fluorescein isothiocyanate (FITC)-labeled dextrans and proteins (molecular mass 4-2000 kDa) at 25 degrees C and with fluorescent microspheres (207 nm diameter) over a temperature range of 5-50 degrees C. Lateral diffusion coefficients (D) were independent of the focus position, and the degree and extent of bleach. The free diffusion coefficient (Do) of FITC-aggrecan determined by confocal FRAP was 4.25 +/- 0.6 x 10(-8) cm2 s-1, which is compatible with dynamic laser light scattering measurements. It appeared to be independent of concentration below 2.0 mg/ml, but at higher concentrations (2-20 mg/ml) the self-diffusion coefficient followed the function D = Do(e)(-Bc). The concentration at which the self-diffusion coefficient began to fall corresponded to the concentration predicted for domain overlap. Multimolecular aggregates of aggrecan ( approximately 30 monomers) had a much lower free diffusion coefficient (Do = 6.6 +/- 1.0 x 10(-9) cm2 s-1) but showed a decrease in mobility with concentration of a form similar to that of the monomer. The method provides a technique for investigating the macromolecular organization in glycan-rich networks at concentrations close to those found physiologically.     

Prevalence and impact of risk factors for lower body difficulty among Mexican Americans, African Americans, and whites

BACKGROUND: The purpose of the study was to estimate the prevalence of sociodemographic, health behavior, chronic disease, and impairment factors and their impact on difficulty in lower body function among two age-cohorts (51-61 and 71-81 years) of Mexican Americans, African Americans, and Whites. METHODS: Reports from 8,727 and 4,510 self-respondents of the 1992 baseline Health and Retirement Survey and the 1993 baseline Assets and Health Dynamics Study, respectively, were used to estimate prevalence. Multiple linear regression of the 4-item lower body difficulty scale (alpha = .80) was used to estimate the direct effects of the risk factors within the age-cohort and ethnicity groups. RESULTS: Overall, the risk factors are more prevalent among both minority groups and the older age-cohort. Lower body deficits are particularly high among Mexican Americans and the younger age-cohort of African Americans. The impact of risk factors does not vary much by ethnicity or age-cohort. Female gender, pain, arthritis, and heart and lung disease are the major risk factors, and they account for about one-third of the variance in lower body difficulty for each group. CONCLUSIONS: Efforts to prevent or reduce lower body difficulty should pay particular attention to pain, arthritis, and heart and lung disease. The central role of sociodemographic and behavioral factors in chronic disease argues for their continued inclusion in disability modeling and prevention.     

Radiobiological modeling of combined targeted 131I therapy and total body irradiation for treatment of disseminated tumors of differing radiosensitivity

PURPOSE: A model is presented for calculating combinations of targeted 131I and total body irradiation, followed by bone marrow rescue, in the treatment of tumors of different radiosensitivity. The model is used to evaluate the role of the total body irradiation component in the optimal combination regime as a function of the radiosensitivity of the tumor cells. METHODS AND MATERIALS: A microdosimetric model was used to calculate absorbed dose in small tumors and micrometastases when uniformly targeted by the radionuclide 131I. Cell kill was calculated from absorbed dose using an extended version of the linear quadratic model. The addition of varying total doses of total body irradiation, assuming 2 Gy fractions, was also calculated using the linear quadratic model. The net cell kill from combined modality (targeted 131I and total body irradiation) was computed for varying proportions of the two components, for a range of tumor sizes, restricting the total radiation dose to within tolerance for a full-course TBI regime (approximately 14 Gy total) in all cases. The calculations were repeated for a range of presumed tumor uptakes of the targeting agent and for a range of tumor radiosensitivities, typical of those reported for tumor cells of differing type in culture. Optimal regimes were identified as those predicted to yield a high probable tumor cure rate (evaluated using a Poisson statistical model) for all tumor sizes. RESULTS: The analysis supports earlier model studies which predicted that systemic combination treatment with targeted 131I and total body irradiation would be superior to either component used alone. The intrinsic tumor radiosensitivity is found to be a factor which influences the optimal combination of the 131I and external beam total body irradiation components. The total body irradiation component is greater in optimal regimes treating radio-resistant than radiosensitive tumors. However, an obligatory total body irradiation component is also predicted for more radiosensitive tumors; the analysis suggests that the total body irradiation component should in no circumstances be less than 2 x 2 Gy, whilst practical arguments exist in favor of higher doses. CONCLUSION: Total body irradiation is an obligatory component for effective systemic treatment of disseminated malignant tumors to which 131I can be selectively targeted. Clinical studies applying this strategy to the treatment of neuroblastoma by 131I targeted by meta-iodo-benguanidine (mIBG), total body irradiation and bone marrow rescue are now in progress.