Limited Multiplication of Symbiotic Cyanobacteria of Azolla spp. on Artificial Media

We examined various media and conditions to isolate symbiotic cyanobacteria from the leaf cavities of Azolla spp. Cyanobacteria survived and multiplied to a limited extent on a medium with fructose, Casamino Acids, yeast extract, and NaNO₃ under 1% O₂. These cyanobacteria were antigenically identical to the endosymbionts.     

Evidence for cytosolic benzo(a)pyrene carrier proteins which function in cytochrome P450 oxidation in rat liver

Solutions of cytosolic proteins from rat liver contain benzo(a)pyrene solubilizing activity capable of serving as a carrier between solid state benzo(a)pyrene and microsomal cytochrome P₄₅₀. Fractionation of benzo(a)pyrene-saturated cytosolic proteins on a Sephadex G-100 column or by sucrose density gradients produced benzo(a)pyrene peaks of about 46,000 daltons and a very high molecular weight material. The protein-bound benzo(a)pyrene obtained in both peaks was oxidized rapidly by microsomes in the presence of NADPH, indicating that the benzo(a)pyrene carrier activity is capable of presenting the substrate to the cytochrome P₄₅₀. Liver cytosolic proteins from rats receiving intraperitoneal injection of [¹⁴C] benzo(a)pyrene was chromatographed on a column of Sephadex G-75. Radioactivity eluted at the same positions of the chromatogram as did the carrier activities described above. These results indicate that these benzo(a)pyrene carrier proteins may have an $\text{in}\text{vivo}$ role in the metabolism of benzo(a)pyrene.     

Evolution in the structure and function of carboxyl proteases

Summary A model for the structure and function of extracellular carboxyl (acid) proteases can be established from three amino acid sequences and four crystal structures of these enzymes. The carboxyl proteases from gastric and fungal origins are very homologous in both primary and tertiary structures. The molecules consist of about 320 residues organized with a secondary structure which is primarily comprised of -strands and very similar tertiary structures. An apparent binding cleft, which can accommodate a substrate with about eight amino acid residues, contains near its midpoint the active center residues Asp-215, Asp-32, and Ser-35. These three residues are hydrogen bonded to each other.An intracellular carboxyl protease, cathepsin D, is very homologous to the extracellular enzymes in N-terminal amino acid sequence and primary structure location of active center residues. The tertiary structure of cathepsin D is probably similar, as well. However, cathepsin D contains a unique hydrophobic tail made up of about 100 residues added on the C-terminal side. Cathepsin D precursor is over 100,000 daltons in molecular weights, as contrasted to the gastric carboxyl protease zymogens, which are about 40,000 daltons.     

Photochemical activation of Rana pipiens tyrosinase

Purified tyrosinase from $\text{Rana pipiens}$ is activated by light. An action spectrum for the process indicates that there are two absorption bands responsible for the activation (290nm and 334nm). The kinetics of the photochemical process show an initial activation followed by inhibition. Molecular oxygen is required. The ability of the protein to be photoactivated and the absorbancy of the protein at 334nm can be extracted with 50% acetone/water.     

Mechanism of intramolecular activation of pepsinogen. Evidence for an intermediate delta and the involvement of the active site of pepsin in the intramolecular activation of pepsinogen.

Intramolecular pepsinogen activation is inhibited either by pepstatin, a potent pepsin inhibitor, or by purified globin from hemoglobin, a good pepsin substrate. Also, pepsinogen at pH 2 can be bound to a pepstatin-Sepharose column and recovered as native zymogen upon elution in pH 8 buffer. Kinetic studies of the globin inhibition of pepsinogen activation show that globin binds to a pepsinogen intermediate. This interaction gives rise to competitive inhibition of intramolecular pepsinogen activation. The evidence presented in this paper suggests that pepsinogen is converted rapidly upon acidification to the pepsinogen intermediate delta. In the absence of an inhibitor, the intermediate undergoes conformational change to bind the activation peptide portion of this same pepsinogen molecule in the active center to form an intramolecular enzyme-substrate complex (intermediate theta). This is followed by the intramolecular hydrolysis of the peptide bond between residues 44 and 45 of the pepsinogen molecule and the dissociation of the activation peptide from the pepsin. Intermediate delta apparently does not activate another pepsinogen molecule via an intermolecular process. Neither does intermediate delta hydrolyze globin substrate.     

污水处理厂生物气溶胶抗生素抗性污染特征、来源及潜在风险

污水处理厂是抗生素抗性基因（antibiotic resistance genes,ARGs）和抗生素抗性细菌（antibiotic resistant bacteria,ARB）重要的源和汇,生物气溶胶是ARGs和ARB自污水处理厂向周边环境释放的关键载体。目前缺乏对污水处理厂生物气溶胶抗生素抗性污染特征、来源及潜在风险的系统性总结。本文从采样方法、检测方法、逸散特征、来源、潜在危害和风险评估等方面对污水处理厂抗生素抗性污染研究现状进行综述。惯性采样法和过滤法是常用的污水处理厂抗生素抗性生物气溶胶主要采集方法,而宏基因组测序、组装和分箱为其ARGs组成、可移动性和宿主提供了有效的检测方法,抗多药类、抗杆菌肽类、抗氨基糖苷类、抗四环素类、抗β-内酰胺类、抗磺胺类、抗大环内酯类和抗糖肽类等抗性基因在污水处理厂PM₁₀、PM_2.5和PM_1.0颗粒物中广泛检出。格栅间、生化反应池和污泥处理单元是污水处理厂PM₁₀、PM_2.5和PM_1.0负载ARGs和ARB的主要释放单元。污水处理厂不同粒径生物气溶胶中致病性ARB的存在增加了抗生素治疗的难度,而污水和污泥对ARGs和ARB的释放起到了重要的源的贡献。本文在研究内容、研究技术和控制策略等方面也提出了相关展望,以期为污水厂生物气溶胶抗生素抗性污染的监测和防护提供参考和借鉴。