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.     

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.     

活菌制剂活菌数急剧衰降的原因与减缓衰降的方法

市售活菌制剂口服液活菌数急剧衰降的原因是营养缺乏,特别是缺乏部分氨基酸及某些维生素。增加动物性蛋白胨及强化酵母膏,添加适量维生素可使活菌数一年后保持在１０^６／ｍｌ以上。     

Quantitative regulation of the thermal stability of enveloped virus vaccines by surface charge engineering to prevent the self-aggregation of attachment glycoproteins

The development of thermostable vaccines can relieve the bottleneck of existing vaccines caused by thermal instability and subsequent poor efficacy, which is one of the predominant reasons for the millions of deaths caused by vaccine-preventable diseases. Research into the mechanism of viral thermostability may provide strategies for developing thermostable vaccines. Using Newcastle disease virus (NDV) as model, we identified the negative surface charge of attachment glycoprotein as a novel determinant of viral thermostability. It prevented the temperature-induced aggregation of glycoprotein and subsequent detachment from virion surface. Then structural stability of virion surface was improved and virus could bind to and infect cells efficiently after heat-treatment. Employing the approach of surface charge engineering, thermal stability of NDV and influenza A virus (IAV) vaccines was successfully improved. The increase in the level of vaccine thermal stability was determined by the value-added in the negative surface charge of the attachment glycoprotein. The engineered live and inactivated vaccines could be used efficiently after storage at 37°C for at least 10 and 60 days, respectively. Thus, our results revealed a novel surface-charge-mediated link between HN protein and NDV thermostability, which could be used to design thermal stable NDV and IAV vaccines rationally.