Microbial models of mammalian metabolism: microbial reduction and oxidation of pentoxifylline.

Fourteen microorganisms, including fungi, yeasts, and bacteria, were screened for their ability to metabolize the xanthine drug pentoxifylline. Thirteen cultures either reduced the drug to the alcohol metabolite or oxidatively cleaved the ketonic side chain to homologous carboxylic acid metabolites. The alcohol metabolite was the predominant or sole metabolite in all organisms, with conversions ranging from 6 to 91%. Preparative-scale production of the alcohol metabolite with Rhodotorula rubra (ATCC 20129) allowed for the isolation of this product with a 40% yield. Two organisms also produced the carboxylic acid metabolites at low levels (2 to 10%). The routes of metabolism in microbial cultures are the same as those reported in mammalian systems.     

Stereoselective hydroxylation at the aliphatic carbons of 7,8- and 9,10-dihydrobenzo[a]pyrenes by rat liver microsomes

Optically active 7-hydroxy-7,8-dihydrobenzo[a]pyrene and 8-hydroxy-7,8-dihydrobenzo[a]pyrene were identified as two of the major metabolites formed by incubation of 7,8-dihydrobenzo[a]pyrene with rat liver microsomes. Optically active 9-hydroxy-9,10-dihydrobenzo[a]pyrene and 10-hydroxy-9,10-dihydrobenzo[a]pyrene were similarly identified as two of the minor metabolites of 9,10-dihydrobenzo[a]pyrene. The formation of these metabolites was abolished either by prior treatment of liver microsomes with carbon monoxide or the absence of NADPH, but was not inhibited by an epoxide hydrolase inhibitor. The results indicate that the aliphatic carbons of dihydro polycyclic aromatic hydrocarbons may undergo stereoselective hydroxylation reactions catalyzed by the cytochrome P-450 system of rat liver microsomes.     

Colorimetric determination of microgram quantities of polylysine by trypan blue precipitation

A simple and sensitive method for the determination of polylysine in solution is described. Polylysine is quantitatively precipitated with trypan blue. The absorbance of unbound dye in the supernatant is inversely proportional to the concentration of this polyamino acid. The precipitation is identical for all sizes of polylysine of molecular weight 13,000 or higher, and is prevented by the addition of either polyanions or serum. The measurable range of polylysine hydrobromide is between 1 and 10 micrograms/ml, which is about 10-fold lower than that by the published methyl orange precipitation method.     

A missense mutation (G197→A) in theα-l-fucosidase gene of fucosidosis patients leads to loss ofα-l-fucosidase

Fucosidosis is an autosomal recessive lysosomal storage disease resulting from the absence of -l-fucosidase activity. Two natural missense mutations (G¹⁹⁷A) and (A⁸⁶⁰G) within the -l-fucosidase gene have been reported to be homozygous in four patients with fucosidosis. Expression of wild-type and mutated -l-fucosidase cDNAs in COS-1 cells revealed complete deficiency of -l-fucosidase for the G¹⁹⁷A transition and a normal level of enzyme for A⁸⁶⁰G. We therefore conclude that the change of G¹⁹⁷A is responsible for fucosidosis in the patients while A⁸⁶⁰G is a normal polymorphic variant of -l-fucosidase.     

砷对农田生态系统污染效应的试验研究

本文通过盆栽及模拟试验,研究了砷对农田生态系统中农作物、土壤微生物、土壤动物的污染效应。结果表明,砷对农作物生长发育有明显不良影响,浓度过高,产量下降并造成农作物体内砷的残留累积;不同种类农作物对砷的敏感程度不同,以对水稻的危害最严重,其次为春小麦、玉米;不同形态砷化物的污染效应有显著差别,亚砷酸盐的毒性最强,砷酸盐次之,硫化砷的影响最小。 砷对土壤微生物具有明显抑制作用,使土壤细菌总数降低,投加亚砷酸钠5ppm,砷酸氢二钠10ppm时,细菌总数开始减少。对土壤固氮菌、解磷细菌、纤维分解细菌等土壤有益微生物有明显抑制作用,使存活率下降。砷污染土壤活性降低,土壤呼吸强度下降。 砷污染影响土壤中蚯蚓的数量与分布,当砷在100—300ppm时,可使蚯蚓致死,死亡率达50—80％。砷在蚯蚓体内明显富集,富集系数为1.32—7.44。     

植物群落种群分布格局研究的新方法

本文给出一种研究植物群落种群分布格局的新方法。该方法与英国著名生态学家Greig-Smith提出的“邻接格子样方法”相比较,具有如下优点: 1.用计算机算出的结果,具有令人满意的精度。当计算完毕后,机器能打印输出植物种群斑块大小、斑块在样地平面上分布的状况,样地上某种植物斑块的总面积,种群个体的总数等有关信息。 2.适用于天然植物群落种群分布格局的研究。 本文讨论了处理数据时采用的计算公式,所依据的数学原理以及如何确定输出界限(舍入界限)等问题。 此外,文中还叙述了用该法对随机相嵌几何斑块图形,人工模拟草地样方进行处理的过程和计算结果分析。 源程序是用BASIC语言编制的。