果胶甲酯酶的结构与功能研究进展

果胶甲酯酶(PME)是一种重要的果胶酶,其水解果胶中的甲酯基从而释放甲醇并降低果胶的甲酯化程度。目前在食品加工、茶饮料、造纸等生产工艺中有着广泛的应用前景。随着对PME的深入研究,已报道了几种不同来源的酶晶体结构,对这些已获得的晶体结构进行分析发现,PME属于右手平行β-螺旋结构,其催化残基为2个保守的天冬氨酸和1个谷氨酰胺残基,并且在催化过程中分别起到了一般酸碱、亲核试剂以及稳定中间体的作用。同时对其底物特异性进行分析,初步了解其底物与活性位点的识别机制。文中针对这几个相关方面进行了系统的综述。     

Further evidence for distinction between sex hormone-binding globulin and an androgen-binding protein in hydatidiform mole serum

We further studied the androgen-binding protein (ABP) that we recently evidenced in the serum from two patients with hydatidiform mole [Ref. 4]. This protein was further shown to be distinct from the sex hormone-binding globulin (SHBG) by concanavalin A and ion-exchange chromatographies, as well as spectrophotometric and kinetic studies. However, the ABP was shown to have a molecular weight and relative affinities for several steroids, similar to those of SHBG.Our results lead us to suppose that the ABP previously evidenced in molar vesicles and fluid [Ref. 5] is secreted in the serum. It is, however, likely that the secretion process alters the binding affinity of this protein. The presence of this additional binding component in the serum of patients with such trophoblastic tumours, may reduce severely the free 17β-hydroxyandrogens levels, as well as may help create a release gradient in the serum steroids buffer stores.     

The transmission of learned behavior: An observational study of father-child interactions during fishing

Mechanisms of transmission of learned behavior were described in terms of the behavioral interactions between fathers and their children as they fished from a pier on Maryland's Eastern Shore. Verbal and nonverbal behaviors and the patterns of association in the behavioral repertoire were described in detail. Groupings of associated behaviors ranged from clusters suggestive of modeling or simple showing to complex combinations of behaviors involved in teaching. There were indications that the transmission behaviors varied with the content of the transmitted information and the role of the performer. Role differentiation in the transmission behaviors suggested the occurrence of two distinct patterns in the ontogeny of complex behaviors.     

Intermediary metabolism of estriol in pregnancy

Estriol (E₃), the most abundant estrogen in pregnancy is produced predominantly in the placenta from androgen precursors of fetal origin. The estriol so formed is secreted efficiently into the maternal circulation where it is converted to 4 conjugates—estriol-3-sulfate (E₃-3S), estriol-16-glucosiduronate (E₃-16G), estriol-3-glucosiduronate (E₃-3G) and estriol-3-sulfate-16-glucosiduronate (E₃-SG). The order of renal clearances is E₃-16G > E₃-3G > E₃-3S ~ E₃-SG. Unconjugated E₃ and E₃-3G differ from the other forms of estriol in that their removal from the blood compartment is essentially irreversible. E₃-3S, E₃-16G and E₃-SG undergo interconversions during enterohepatic circulation and eventual partial conversion to E₃-3G. Following delivery of the fetus and placenta, unconjugated E₃ is no longer detectable in the maternal serum within l–2h, whereas the concentrations of the conjugates decline more slowly, the rates being determined by the rates of renal clearance and enterohepatic interconversions. E₃-3G levels were dramatically elevated in a case of Group C polycystic kidney disease, providing evidence that this conjugate is indeed an end-product of estriol metabolism.     

Inhibition of the UV induction of sister-chromatid exchanges in ICR-2A frog cells by pretreatment with γ-rays

Exposure of ICR-2A cells to UV induced the formation of sister-chromatid exchanges (SCEs). However, pretreatment of UV-irradiated cells with γ-rays resulted in a reduction in the level of SCEs. This effect was observed over a range of UV fluences (1–5 J/m²) and γ-ray doses (50–500 rad). In addition, the deprassion of UV-induced SCEs was greatest when the UV treatment was performed within 3 h after γ-irradiation. At later times the level of SCEs approached that of cells exposed only to UV.     

中国国家森林公园碳储量及固碳速率的时空动态

森林生态系统在调节气候变化和维持碳平衡中具有重要作用.国家森林公园是森林保护的主要载体,探明其碳储量和固碳速率的变化对于森林生态系统的固碳能力评估和可持续经营管理具有重要意义.本研究采用生态系统过程模型CEVSA2模型,模拟了1982-2017年中国881处国家森林公园的碳密度、碳储量和固碳速率的空间分布特征.结果 表...     

Properties of a local anesthetic receptor in rat brain

Saturable binding of local anesthetics in rat brain homogenates was demonstrated using (14C)-lidocaine and (3H)-bupivacaine. Saturation analyses revealed a single class of binding sites for lidocaine and bupivacaine. A series of drugs with local anesthetic properties inhibited this binding, while drugs without local anesthetic activity did not affect the specific binding. Specific binding of lidocaine and bupivacaine was maximal from pH 8 to 10; the pH versus binding profile was similar to that reported for local anesthetic blocking of peripheral nerve conduction. These characteristics suggest that binding of local anesthetics to this or similar sites mediates their pharmacological activity.     

Phosphorylated proteins from anuran intestinal microvilli membranes--I. Relations with alkaline phosphatase

The degree of phosphorylation of intestinal microvilli membrane proteins in an adult amphibian, Rana esculenta, was investigated under various experimental conditions. The microvilli protein phosphorylation rate rapidly increases during the first 4 min of incubation in a medium containing [gamma-32P]ATP. This increase is slower afterwards. Cyclic nucleotides (cyclic AMP, cyclic GMP) and sorbitol do not modify the microvilli protein phosphorylation rate. On the contrary, this phosphorylation rate significantly decreases in the presence of L-lysine, when its concentration in the incubation medium is greater than 25 mM. The time course of phosphorylation confirms the inhibitory effects of L-lysine (100 mM). The microvilli membrane proteins were distinguished by polyacrylamide gel electrophoresis. In heated samples, electrophoresis followed by an radioautograph systematically reveals the existence of a very phosphorylated protein with a mol. wt of 86 kDa. The phosphorylation of this protein is partially inhibited by L-lysine (100 mM). The very phosphorylated protein could be the monomer of alkaline phosphatase. The dimer (170 kDa) is visualized on electrophoretograms by its catalytic activity. In mammals, several authors have established a correlation between phosphorylation of the microvilli membrane proteins and the intensity of intestinal calcium absorption. Such a control is presently being investigated in adult Rana esculenta.     

耕作措施对土壤水热特性和微生物生物量碳的影响

通过山西寿阳设置的8a田间定位试验,比较了全量秸秆还田、免耕覆盖和常规耕作3种耕作措施下土壤含水量、温度及土壤微生物生物量碳变化.结果表明:免耕覆盖与全量还田处理显著提高土壤含水量,与常规耕作相比表层土壤体积含水量在玉米苗期、拔节期、灌浆期和成熟期分别高出18％、22％、29％、21％和3％、10％、12％、13％,具有保水保墒的作用.在苗期不同耕作措施对土壤温度的影响达到显著水平,5 cm处免耕覆盖、全量还田与常规耕作处理土壤温度依次为:18.12、18.76和19.44℃,免耕覆盖和全量还田处理平均温度比常规耕作分别低1.32℃和0.69℃.土壤微生物量碳在整个生育期动态变化是首先迅速上升在玉米生育高峰期(拔节期)达到最高峰,然后开始下降,成熟期趋于平缓.免耕覆盖与全量还田处理下玉米各生育期土壤表层微生物量碳显著高于常规耕作,在苗期、拔节期、灌浆期和成熟期分别比常规耕作高出70％、40％、85％和30％和10％、20％、15％和15％.土壤微生物量碳与土壤温度和土壤含水量相关和极相关.