Ribamidil as a modulator of the toxic effect of 5-fluorouracil

The in vitro experiments on CaOv cells demonstrated that ribamidyl (ribavirine) (Rb) enhances the intracellular pool of pyrimidine precursors of DNA. This was the basis for studies of its modifying effect on the antitumour activity of antimetabolites. In experiments with intact hybrid mice F1 (CBA+C57B1) the five times administration of ribavirine increase sharply the toxicity of 5-FU. The data should be taken into consideration when combining Rb with antimetabolites in clinical practice.     

Mycobacterium smegmatis fatty acid synthetase. Polysaccharide stimulation of the rate-limiting step

An initial activity burst lasting 5 to 10 s is observed for both de novo synthesis with acetyl-CoA as primer and for elongation of palmitoyl-CoA catalyzed by the multienzyme complex fatty acid synthetase from Mycobacterium smegmatis. After the initial burst, synthetase activity slows at least 6-fold to the steady state rate. The size of the initial burst is proportional to the amount of synthetase protein and corresponds to the synthesis of a small number C three to five) of C24 or C26 acyl chains per mol of enzyme. During the initial burst, C24, C26 acyl enzyme is formed and can be isolated by ammonium sulfate precipitation. On incubation with CoA, enzyme-bound acyl chains undergo transacylation to form the corresponding CoA derivatives. Diffusion of C24-CoA and C26-CoA from the enzyme is slow and rate-limiting for overall fatty acid synthesis. Mycobacterial polysaccharides markedly accelerate this rate-determining step but bovine serum albumin does not. This facilitation of product diffusion accounts for the large stimulation of de novo synthesis and of elongation of mycobacterial polysaccharide. It is also shown that the high apparent Km for acetyl-CoA (approximately 400 micrometer) in the steady state reflects the substrate concentration required to shift the product pattern in favor of shorter chain fatty acids (C16,C18). These conditions circumvent the slow, rate-limiting diffusion of C24-CoA and C26-CoA.     

DERIVING PLACE-SPECIFIC MEASURES OF THE RENTAL HOUSING CRISIS FROM THE 1980 CENSUS: AN APPLICATION FROM TEXAS

The argument is advanced that rental affordability problems are the key symptom of the rental housing crisis. These problems may be measured by the rent-to-income ratio as reported by the 1980 census for five different income groups. Of special significance is that these data are available in a standardized form for every county, city and census tract in the nation. To demonstrate the use of these data, a rent burden indicator is constructed from these data and then applied to all counties in Texas with at least 100,000 population. One county, Travis, stands out with a particularly high incidence of rent burden, and this incidence is only slightly reduced when the rent burden indicator is adjusted to a standardized income distribution. This provides clear evidence of an unusually severe rental housing crisis.     

Mycobacterium smegmatis fatty acid synthetase. Long chain transacylase chain length specificity

Long chain transacylase activity, acyl-CoA + enzyme in equilibrium acyl-enzyme + CoA, catalyzed by the multienzyme complex fatty acid synthetase from Mycobacterium smegmatis was measured by exchange of radioactive coenzyme A into even numbered fatty acyl-CoA substrates 14 to 24 carbon atoms long. This transacylase activity decreases sharply with increasing chain length. It is suggested that C24 transacylation may be rate-limiting in de novo fatty acid synthesis catalyzed by the myocobacterial system. Mycobacterial polysaccharides stimulate the rate of transacylation, and this enhancement becomes more marked as the chain length of the substrate increases. The magnitude of the effect is similar to polysaccharide stimulation of overall synthetase activity. It is therefore proposed that terminal transacylation is the specific and perhaps only partial reaction catalyzed by the M. smegmatis fatty acid synthetase which is facilitated by polysaccharide. The product distribution of the synthetase is distinctly bimodal, with peaks for acyl chains 16 and 24 carbon atoms long. A scheme based on nonoverlapping unimodal chain length specificities for the rates of two activities, elongation and terminal transacylation, is offered to explain this bimodal distribution.     

Rectangular Pulse Generation Based on High-Voltage Transistor Switches Operating in Synchronous and Asynchronous Modes

Instruments and Experimental Techniques - Two modes (synchronous and asynchronous) of operation of a high-voltage pulse generator, which is based on parallel-connected high-voltage switches (HVSs)...     

无卤阻燃PC/ABS的制备及燃烧性能

以齐聚磷酸酯(BDP)作为添加型阻燃剂制备了阻燃PC/ABS塑料合金,采用锥形量热仪(CONE)、扫描电镜(SEM)及热裂解-气相/质谱法(Py-GC/MS)等对材料的燃烧性能和阻燃机理进行了研究.结果表明,阻燃剂BDP对PC/ABS有良好的阻燃效果;BDP的加入使PC/ABS燃烧残留物上产生大量的致密微孔,同时由Py-GC/MS分析表明BDP的加入降低了PC/ABS可燃性降解产物的生成,裂解产物中含有三苯基磷酸酯(TPP),说明BDP在塑料合金降解过程中分解生成TPP发挥阻燃作用.