Pipecolic Acid Hydroxylases: A Monophyletic Clade among cis‐Selective Bacterial Proline Hydroxylases that Discriminates l‐Proline

Proline hydroxylases are iron(II)/2‐oxoglutarate‐dependent enzymes that hydroxylate l ‐proline and derivatives, such as l pipecolic acid, which is the six‐membered‐ring homologue of l ‐proline. It has been established that there is a distinct group of conserved bacterial enzymes that hydroxylate l ‐pipecolic acid and trans‐3‐ and trans‐4‐methyl‐l ‐proline, but virtually no l ‐proline. This allows the organism to produce hydroxyproline congeners without hydroxylation of the physiologically omnipresent l ‐proline. In vitro conversions showed that the substrate spectrum of the pipecolic acid hydroxylases GetF (from a Streptomyces sp.; producer of the tetrapeptide antibiotic GE81112) and PiFa (from Frankia alni) overlaps that of proline hydroxylases, except for the nonacceptance of l ‐proline and smaller homologues. Distinct and conserved residues were determined for both types of enzymes. However, site‐directed mutagenesis in GetF did not yield variants that accepted l ‐proline; this suggested a complex interaction of several residues around the active site, which resulted in delicate changes in substrate specificity. This is supported by substrate docking in a homology model of GetF, which revealed an altered orientation for l ‐proline relative to that of preferred substrates.     

原位固化黑荆树单宁对La3+、Pr3+、Nd3+的吸附特性

以富含单宁的黑荆树树皮为原料,通过甲醛交联剂原位固化黑荆树单宁制备吸附材料,研究该吸附材料对轻稀土离子La3+、Pr3+、Nd3+ (RE3+)的吸附特性。实验表明：该吸附材料对La3+的吸附最适宜的pH为5.0左右,对Pr3+、Nd3+的吸附最适宜的pH为5.5左右,此时pH升高或降低,吸附量有较大幅度下降。和pH因素的影响相比较,温度对平衡吸附量影响较小,反应温度为303 K时,原位固化黑荆树单宁对RE3+的吸附效果最好。当RE3+溶液的初始浓度为5.0 mmol·L-1时,在温度为303 K和最适宜的pH条件下,吸附剂用量为0.10 g, 平衡吸附量可达到La3+为217.26 mg·g-1,Pr3+为228.56 mg·g-1,Nd3+为329.76 mg·g-1,其吸附等温线符合Freundlich方程。这种吸附剂对RE3+的吸附动力学可用拟二级速率方程来描述,由拟二级速率方程计算所得到的平衡吸附量与实测值的偏差在7%以内,具有很好的一致性。     

杀青条件对酶法提取南瓜果胶影响的研究

探讨了对纤维素酶法提取南瓜果胶效果有影响的两个杀青条件———温度和时间,并研究了优化工艺条件的放大过程。结果表明:杀青温度为85℃,杀青时间为20 min为最佳提取工艺,提取得率为14.3%。在放大15倍的实验中,提取得率为21.4%,这可能是由于放大实验中的测量误差减少所致。实验所得到的最佳果胶提取条件可以为综合利用南瓜提供一定的实验依据。     

去除铁锰离子微生物活性滤料的研制

探索在复合载体中添加粉煤灰、麸皮,活性炭制备固定化小球,通过包埋铁锰氧化细菌(节杆菌),用于处理含铁锰的原水,并以水体中铁锰去除率为指标考察影响铁锰去除的各种因素,通过试验优化了固定化小球的制备条件。结果表明,当菌体含量70 g/L,粉煤灰20 g/L,活性炭粉30 g/L,麸皮10 g/L,在此条件下制作的固定化小球作用于Mn2+、Fe2+质量浓度分别为30 mg/L、100 mg/L的原水,2 d后铁去除率为100%,7 d锰去除率为99.02%,显示出较好的除铁锰性能。固定化小球去除铁锰的较适宜pH为7,增加小球用量可进一步提高铁锰去除率。在一定范围内,提高Fe2+初始浓度可促进锰的去除。     

聚乙烯醇作为固定化细胞包埋剂的研究

以聚乙烯醇为包埋剂 ,探索其制备固定化细胞小球的工艺过程 ,着重从小球颗粒的机械强度、传质性能及微生物活性等三个方面来选择其最适宜的包埋条件。最后 ,还对固定化细胞的保存进行了试验研究     

固定化细胞技术在废水处理中的应用

介绍了固定化细胞技术,综述了近年来固定化细胞的制备方法、固定化细胞的反应特性,对采用细胞固定化技术处理各种废水的一些实验模拟进行了简要的论述,并指出了今后的研究方向。     

Naringinase Immobilization in Packaging Films for Reducing Naringin Concentration in Grapefruit Juice

Naringin, a bitter compound in citrus, may be converted to a nonbitter form by enzymic hydrolysis. Our objective was to determine the feasibility of immobilizing naringinase in a food contact approved packaging film. Naringinase from Penicillium sp. was immobilized in cellulose acetate films with up to 23% efficiency at 7°C. Kinetic studies showed that the free enzyme had an optimum pH=3.5 and the immobilized enzyme pH=4.0. Activation energy decreased upon immobilization (from 14.2 to 11.0 Kcal/mol), thus providing an increased catalytic efficiency for immobilized naringinase. The Michaelis constant for immobilized naringinase (K_m=2.1 mM) was lower than for free enzyme (K_mm=3.6 mM). Keeping films under dry storage for 1 mo at room temperature did not cause decreased enzyme activity. A film area/volume ratio (cm²/mL of 10° Brix grapefruit juice) of 7.2 hydrolyzed 60% of the naringin in 15 days at 7°C.     

Decalepis hamiltonii roots boost antioxidant status of rat liver and brain

BACKGROUND: Roots of Decalepis hamiltonii are traditionally consumed as pickles and juice for their health benefits. We have earlier demonstrated the antioxidant property of the root extract and identified the constituent antioxidant molecules. RESULTS: This paper reports the effect of multiple‐dose (7, 15, and 30 days) treatment of Decalepis hamiltonii aqueous root extract (DHA) (50 and 100 mg kg^?1 body weight) on the antioxidant profile of rat liver and brain. Activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione‐S‐transferase (GST) were increased and glutathione content was elevated in both liver and brain, apart from reduction in the basal level of lipid peroxidation. DHA induced stronger antioxidant boost in brain by increasing the activities of SOD, CAT, and GPx compared to liver. CONCLUSION: As failure to grapple with oxidative stress is an important factor in the etiology of several diseases, DHA's effects on improvement of antioxidant status could provide a scientific justification for the health‐promoting properties attributed to it. Copyright © 2009 Society of Chemical Industry