一种快速、灵敏的血小板释放功能检测方法及其在抗血小板药物研究中的应用

本文报道了一种快速、灵敏的血小板释放功能检测方法:利用荧光素-荧光素酶在有ATP、Mg~(2+)、O_2存在时产生的生物发光素测定血小板ATP的释放量,以反映血小板的释放功能;研究了ADP、AA、胶原、凝血酶等四种诱导剂对血小板释放功能的作用,发现ADP的诱导释放能力较其他三者为弱;观察在不同剂量ADP和AA的诱导下,血小板聚集强度和释放能力之间的关系,研究了血小板数等因素对ATP释放功能测定的影响。应用该方法研究了Aspirin及活血化淤药物川芎嗪,毛冬青甲素对血小板释放功能的影响,发现Aspirin对AA诱导的释放反应有强烈的抑制作用。在以ADP诱导的释放反应中,川芎嗪的抑制作用较毛冬青甲素更为强烈。     

Effects of exercise on insulin binding and glucose metabolism in muscle

To elucidate the mechanism of enhanced insulin sensitivity by muscle after exercise, we studied insulin binding, 2-deoxy-D-[1-14C]glucose (2-DOG) uptake and [5-3H]glucose utilization in glycolysis and glycogenesis in soleus and extensor digitorum longus (EDL) muscles of mice after 60 min of treadmill exercise. In the soleus, glycogenesis was increased after exercise (P less than 0.05) and remained sensitive to the action of insulin. Postexercise insulin-stimulated glycolysis was also increased in the soleus (P less than 0.05). In the EDL, glycogenesis was increased after exercise (P less than 0.05). However, this was already maximal in the absence of insulin and was not further stimulated by insulin (0.1-4 nM). The disposal of glucose occurred primarily via the glycolytic pathway (greater than 60%) in the soleus and EDL at rest and after exercise. The uptake of 2-DOG uptake was not altered in the soleus after exercise (4 h incubation at 18 degrees C). However, with 1-h incubations at 37 degrees C, a marked increase in 2-DOG uptake after exercise was observed in the soleus (P less than 0.05) in the absence (0 nM) and presence of insulin (0.2-4 nM) (P less than 0.05). A similar postexercise increase in 2-DOG uptake occurred in EDL. Despite the marked increase in glucose uptake and metabolism, no changes in insulin binding were apparent in either EDL or soleus at 37 degrees C or 18 degrees C. This study shows that the postexercise increase of glucose disposal does not appear to be directly attributable to increments in insulin binding to slow-twitch and fast-twitch muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bovine serum albumin: characterization of a fatty acid binding site on the N-terminal peptic fragment using a new spin-label

A new spin-label, 4-(L-glutamo)-4'-[(1-oxy-2,2,5,5-tetramethyl-3L-pyrrolidinyl )amino]-3, 3'-dinitrodiphenyl sulfone, is shown to bind to one high-affinity binding site on bovine serum albumin (K = 5 X 10(4) M-1, n = 1). Analysis of the binding of the spin-label to the amino-terminal half (peptic fragment PB) and the carboxy-terminal half (peptic fragment PA) of BSA, and their complex (PA-PB), indicates that the spin-label binds to a long-chain fatty acid binding site located on PB. The usefulness of the novel specificity of the spin-label in characterizing this binding site is discussed.     

Column cellulose hydrolysis reactor: Cellulase adsorption profile

Summary A column cellulose hydrolysis reactor was set up using a single passage of cellulase enzyme which was followed with a continuous percolation of buffer. Hydrolysis rates were found to decline precipitously upon the removal of the non-adsorbed cellulase components. By comparing specific activities of the cellulase before and after adsorption on the cellulose column, it was concluded that the adsorption efficiencies for the cellulase components decreased from exoglucanase (1,4--d-glucan cellobiohydrolase EC 3.2.1.91) to endoglucanase [1,4-(1,3;1,4)--d-glucan 4-glucanohydrolase, EC 3.2.1.4] to -glucosidase (-d-glucoside glucohydrolase, EC 3.2.1.21). Of the adsorbed cellulase components, the rate of endoglucanase leaching from the cellulose column was 20 times that for the exoglucanase despite the greater adsorption efficiency of the latter. By analysing the cellulase components which were bound and not bound by the cellulose column and comparing them with a purified exoglucanase enzyme on sodium dodecyl sulfate polyacrylamide gels, it was confirmed that the major cellulase component adsorbed to the cellulose column was an exoglucanase component. The resultant loss of other cellulase components from the reactor was probably the cause for the much reduced rate of cellulose hydrolysis when these components were flushed out of the column.     

Column cellulose hydrolysis reactor: An efficient cellulose hydrolysis reactor with continuous cellulase recycling

Summary The use of a column cellulose hydrolysis reactor with continuous enzyme recycling was demonstrated by incorporating a continuous ultrafiltration apparatus at the effluent end of the column reactor. Using this setup, over 90% (w/v) cellulose hydrolysis was achieved, resulting in an average sugar concentration of 6.8% (w/v) in the effluent stream. The output of the system was 1.98 g of reducing sugar/l/h with a ratio of 87% (w/v) of the reducing sugars being monomeric sugars. Batch hydrolysis reactors were less effective, resulting in 57% (w/v) of the cellulose being hydrolyzed. The output of the batch reactor was 1.33 g of reducing sugar/l/h with similar product concentrations and percentage of monomeric sugars. The ratio of reducing sugar/filter paper unit of cellulase activity for the column method was 69.1 mg/U as compared to only 21.2 mg/U for the batch reactor.     

The significance of the aprotic solvent in monomer studies related to the primary subunit environment in the macromolecule

An advantage of aprotic polar solvent systems in the study of monomer interactions relevant to the macromolecular state is demonstrated with the measurement of nucleoside amino proton exchange rates in DMSO/water mixtures. The DMSO/water solvent provides the first unequivocal observation of general acid catalysis of nucleic acid amino proton exchange, which is undetectable in aqueous solution due to the formation of the endocyclic protonated nucleobase. Suppression of nucleobase protonation in the presence of buffer acid is a consequence of anion desolvation in the aprotic solvent. The detected route of general acid catalysis is demonstrated as a consequence of Watson-Crick H-bonding, leading to the implication that amino chemistry is modulated in the helical state to decrease amino proton lifetime in the closed macromolecular context of conformational information obtained by hydrogen exchange methods. This useful property of the aprotic solvent can be extended to monomeric studies pertaining to specific local site interactions affecting the function and conformation of proteins and nucleic acids.     

Paper replication method for isolation of radiation-sensitive mutants.

A filter paper replication system particularly useful for isolation of radiation-sensitive mutants of pigmented bacteria was devised. The fidelity of replication was high. Adhesion between a paper disk and a properly dried master plate provided adequate contact pressure. The replicas arising from this technique constitute a convenient apparatus for general application in isolation of clones sensitive to a discriminating treatment.     

Postural influence on maternal capillary oxygen and carbon dioxide tension

The effect of posture on maternal capillary blood Po₂ and Pco₂ was studied in pregnant and non-pregnant women. There was a significant decrease of Po₂ (mean 13·0 mm. Hg) and significant decrease of Pco₂ (mean 2·4 mm. Hg) when pregnant women sat up, but these changes did not occur in the non-pregnant. These findings may be relevant to debate on the optimum posture for labour.     

L-乳酸脱氢酶热变性的热力学研究

用差示扫描量热法对L-乳酸脱氢酶的热变性进行了研究(温度扫描范围为290—390K,酶蛋白溶液浓度为0.28—0.72mg蛋白/mg溶液)。实验观察到当酶溶液浓度在0.62—0.72mg蛋白/mg溶液范围内有一个吸热转变,酶溶液浓度小于0.62mg蛋白/mg溶液时有两个未完全分开的吸热转变。 这个酶的量热焓与范德霍夫焓的比远大于1,而接近于2,这表明乳酸脱氢酶的变性过程不是一个简单的两态转变,从热力学和吸热峰的形状、大小分析,可以推断乳酸脱氢酶分子是由两个以弱相互作用相连结的合作结构区组成,而每一个结构区是由两个相互作用很强的亚基组成。也就是说乳酸脱氨酶的变性过程包括两个半独立的合作结构区的转变,每一个结构区的转变都近似一个两态转变,ΔHeal与ΔHvh的比值是随着两个半独立部分相互作用的增强,即蛋白浓度的增加而减小。随着蛋白浓度的减小,蛋白质周围水分子增多,酶分子中两个半独立部分的相对独立性增强,这可由热谱图上一个吸热转变变成两个半独立的转变得到证实。