Inhibition and alternate-substrate studies on the mechanism of malic enzyme

A number of dead-end inhibitors and alternate substrates were examined to gain an understanding of the substrate specificity and mechanism of malic enzyme. Comparison of Ki values for competitive inhibitors suggested that binding of the l-carboxyl of L-malate is by ion pairing with lysine or arginine, while binding of the 4-carboxyl is weaker, and probably of the induced-dipolar type. The 2-hydroxyl hydrogen bonds to a catalytic group, which, when it is protonated, adsorbs the keto form of oxalacetate. Since the only molecule other than L-malate that is oxidized is L-malate-beta-amide, carbon 4 must be trigonal for substrate activity, although a tetrahedral carbon bearing one or two hydroxyl groups gives good binding. Hydroxy groups at carbon 3 contribute to binding, but prevent substrate activity. Hydroxy and ketomalonates are bound more strongly than any of the four carbon acids, suggesting that the latter are bound with some strain. In inhibition studies, pyruvate analogues were competitive vs. pyruvate but noncompetitive vs. malate, while malate analogues were competitive vs. malate and noncompetitive vs. pyruvate. These compounds thus bind to both enzyme-triphosphopyridine nucleotide (E-TPN) and enzyme-reduced triphosphopyridine nucleotide (E-TPNH), but only malate analogues prevent release of TPN, while pyruvate analogues prevent release of TPNH. Ketomalonate and oxalacetate, both of which are slowly reduced by the enzyme in the presence of TPNH and thus must combine in the keto form with E-TPNH,, appear to combine with E-TPN mainly in the gem-diol (or for oxalacetate, also the enol) form. The substrate for the decarboxylation of oxalacetate at pH 4.5 is the keto form.     

The interaction of test anxiety and success-failure experiences in determining children's arithmetic performance.

Studied the effects of the motives to approach success and to avoid failure in 60 5th and 6th grade boys and girls of low, middle, and high levels of test anxiety (Test Anxiety Scale for Children and Lie Scale for Children). Ss performed addition problems under 1 of 2 conditions: a mixed condition involving two-thirds success and one-third failure under time pressure and a success only condition in which all problems attempted were completed. As predicted, high anxious Ss, when compared to less anxious Ss on response rate, errors, and cheating, showed markedly inferior performance in the mixed condition, but comparable and improved performance in the success only condition. Findings indicate that anxious children perform poorly due to motivational difficulties rather than to learning deficiencies, and that their abilities are systematically underestimated by many achievement and educational testing procedures. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cost-benefit analysis of walking to prevent coronary heart disease

OBJECTIVE: To quantify the cost-benefit relationship of walking to prevent coronary heart disease. DESIGN: Cost-benefit analysis. PARTICIPANTS: Hypothetical cohorts of sedentary men and women aged 35 to 74 years. MAIN OUTCOME MEASURES: Decision-analysis simulation was used to evaluate the cost-benefit relationship of walking, varying level of benefit from exercise, frequency of exercise to achieve benefit, participation rates, and costs of exercise and injury. RESULTS: At a relative risk of 1.9 for heart disease associated with sedentary behavior, $5.6 billion would be saved annually if 10% of adults began a regular walking program. A $4.3 billion savings is predicted if the entire sedentary population began walking regularly and the cost of the time an individual spends exercising is accounted for in those who dislike exercising. According to our baseline assumptions, walking is economically beneficial for men aged 35 to 64 years and for women aged 55 to 64 years. The threshold of relative risk at which economic benefit is found for walking in this population overall is estimated at 1.7, and under a volunteer model, most adults would benefit even at a relative risk of 1.15. CONCLUSIONS: There are significant sex and age differences in the economic benefits of walking to prevent heart disease. The value assigned to the time an individual spends exercising has a significant impact on the results. Overall, a substantial savings is predicted from encouraging sedentary individuals to participate in a regular walking program.     

Treatment of gastritis in cheetahs (Acinonyx jubatus)

Three cheetahs (Acinonyx jubatus) had a clinical history of chronic spiral bacteria-associated gastritis and three cheetahs had no clinical history of gastritis. Gastric biopsies were obtained from all six cheetahs prior to treatment for gastritis and 3 wk and 1 yr posttreatment. The cheetahs were treated with tetracycline hydrochloride 500 mg p.o. q.i.d., metronidazole 250 mg p.o. q.i.d., and bismuth subsalicylate 300 mg p.o. q.i.d. Each drug was administered concurrently for 7 days. Following this treatment, each cheetah was maintained on 300 mg bismuth subsalicylate p.o. s.i.d. for 1 yr. The three cheetahs with a history of gastritis were culture positive for Helicobacter acinonyx and remained positive during the entire study. The three cheetahs with no clinical history of gastritis were culture negative for H. acinonyx, but gastric biopsies revealed Gastrospirillum-like bacteria (tentatively named Helicobacter heilmannii) pretreatment. Gastric biopsies were negative for H. heilmannii on subsequent examinations. Although the treatment did not eradicate H. acinonyx, it did provide symptomatic relief from the vomiting, anorexia, and weight loss associated with clinical gastritis. The use of endoscopically guided gastric mucosal biopsies for urease testing and histopathologic examination of Warthin-Starry-stained sections is a sensitive and specific method of diagnosing spiral bacteria-associated gastritis. Treatment of spiral bacteria-associated gastritis in cheetahs should include the rational use of antibiotics (tetracycline or amoxicillin and metronidazole), bismuth compounds, and omeprazole and evaluation of husbandry methods to reduce stress.     

Neutral shift [five years of continuous operation with adjustable frequency drives]

The combined efforts of the AFD supplier and end-user have resulted in an extremely reliable electrical adjustable speed drive system. Almost three years into the run of the first unit, all parties are confident of the ability to meet the five-year run target that was identified at the outset. The redundancy of the power cells in this particular design, together with the neutral shift control has practically eliminated the power components as a source of operational failure. Future development efforts will include applying redundancy and fault tolerance to the drive control processor to further enhance system reliability.     

Retention behavior of phenols, anilines, and alkylbenzenes in liquid chromatographic separations using subcritical water as the mobile phase

The unique characteristic of subcritical water is its widely tunable physical properties. For example, the polarity (measured by dielectric constant) of water is significantly decreased by raising water temperature. At temperatures of 200-250 °C (under moderate pressure to keep water in the liquid state), the polarity of pure water is similar to that of pure methanol or acetonitrile at ambient conditions. Therefore, pure subcritical water may be able to serve as the mobile phase for reversed-phase separations. To investigate the retention behavior in subcritical water separation, the retention factors of BTEX (benzene, toluene, ethylbenzene, and m-xylene), phenol, aniline, and their derivatives have been determined using subcritical water, methanol/water, and acetonitrile/water systems. Subcritical water separations were also performed using alumina, silica-bonded C18, and poly(styrene-divinylbenzene) columns to study the influence of the stationary phase on analyte retention under subcritical water conditions.     

NanoProbeArrays for the analysis of ultra-low-volume protein samples using piezoelectric liquid dispensing technology

Antibody microarrays are gaining popularity as a high-throughput technology to investigate the proteome. However, protein extracts from most body fluid or biopsy samples are available in very small volumes and are often unsuitable for large-scale antibody microarray studies. To demonstrate the potential for protein analysis with as little as a few nanoliters of sample, we have developed a new technology called NanoProbeArrays based on piezoelectric liquid dispensing for non-contact printing and probing of antibody arrays. Instead of flooding the protein sample on the antibody microarray surface, as in conventional microarray screening, a piezoelectric inkjet printer is used to dispense nanoliters of fluorescently labeled proteins over the antibody spots on the array. The ability of NanoProbeArrays to precisely identify and reliably distinguish between test proteins from different sources, without any loss of sensitivity and specificity as compared with conventional antibody microarrays, is illustrated here. The utility of NanoProbeArrays for biomarker identification in a complex biological sample was tested by detecting the cytokine interleukin-4 in serum. The significant reduction in volume of sample during NanoProbeArray analysis, as compared with conventional antibody microarrays, offers new opportunities for basic and applied proteomic research.