An antimycin-insensitive succinate-cytochrome c reductase activity in pure reconstitutively active succinate dehydrogenase

Antimycin-insensitive succinate-cytochrome c reductase activity has been detected in pure, reconstitutively active succinate dehydrogenase. The enzyme catalyzes electron transfer from succinate to cytochrome c at a rate of 0.7 mumole succinate oxidized per min per mg protein, in the presence of 100 microM cytochrome c. This activity, which is about 2% of that of reconstitutive (the ability of succinate dehydrogenase to reconstitute with coenzyme ubiquinone-binding proteins (QPs) to form succinate-ubiquinone reductase) or succinate-phenazine methosulfate activity in the preparation, differs from antimycin-insensitive succinate-cytochrome c reductase activity detected in submitochondrial particles or isolated succinate-cytochrome c reductase. The Km for cytochrome c for the former is too high to be measured. The Km for the latter is about 4.4 microM, similar to that of antimycin-sensitive succinate-cytochrome c activity in isolated succinate-cytochrome c reductase, suggesting that antimycin-insensitive succinate-cytochrome c activity of succinate-cytochrome c reductase probably results from incomplete inhibition by antimycin. Like reconstitutive activity of succinate dehydrogenase, the antimycin-insensitive succinate-cytochrome c activity of succinate dehydrogenase is sensitive to oxygen; the half-life is about 20 min at 0 degrees C at a protein concentration of 23 mg/ml. In the presence of QPs, the antimycin-insensitive succinate-cytochrome c activity of succinate dehydrogenase disappears and at the same time a thenoyltrifluoroacetone-sensitive succinate-ubiquinone reductase activity appears. This suggests that antimycin-insensitive succinate-cytochrome c reductase activity of succinate dehydrogenase appears when succinate dehydrogenase is detached from the membrane or from QPs. Reconstitutively active succinate dehydrogenase oxidizes succinate using succinylated cytochrome c as electron acceptor, suggesting that a low potential intermediate (radical) may be involved. This suggestion is confirmed by the detection of an unknown radical by spin trapping techniques. When a spin trap, alpha-phenyl-N-tert-butylnitrone (PBN), is added to a succinate oxidizing system containing reconstitutively active succinate dehydrogenase, a PBN spin adduct is generated. Although this PBN spin adduct is identical to that generated by xanthine oxidase, indicating that a perhydroxy radical might be involved, the insensitivity of this antimycin-insensitive succinate-cytochrome c reductase activity to superoxide dismutase and oxygen questions the nature of this observed radical.     

猫脑干上涎核节前神经元电活动的观察

在麻醉的32只猫记录了电刺激颌下腺神经支引起的上涎核平均场电位和单位放电。逆行电刺激颌下腺神经支引起的上涎核平均场电位分布在同侧脑干背面闩部头端5.5—8mm处,与过去的组织学结果大致符合。用微电极在上涎核记录了68个对刺激颌下腺神经支有反应的单位,其中33个单位作了碰撞试验。有9个单位符合逆向反应标准,它们是真正的颌下腺节前神经元,逆行反应的潜伏期为14.4±2.5ms,其轴突传导速度为2.9±0.1m/s。其他不符合逆向反应标准的单位,对刺激颌下腺神经支仍能发生反应,估计多为中间神经元。在一部分单位观察了电刺激舌神经或味觉刺激舌引起的反应。根据这些观察对上涎核内存在复杂神经元回路的可能性作了讨论。     

A mathematical model for the burden of diabetes and its complications

Background  

The incidence and prevalence of diabetes are increasing all over the world. Complications of diabetes constitute a burden for the individuals and the whole society.     

A two-dimensional mathematical model of percutaneous drug absorption

Background  

When a drug is applied on the skin surface, the concentration of the drug accumulated in the skin and the amount of the drug eliminated into the blood vessel depend on the value of a parameter, r. The values of r depend on the amount of diffusion and the normalized skin-capillary clearence. It is defined as the ratio of the steady-state drug concentration at the skin-capillary boundary to that at the skin-surface in one-dimensional models. The present paper studies the effect of the parameter values, when the region of contact of the skin with the drug, is a line segment on the skin surface.     

Immune Related Genes Underpin the Evolution of Adaptive Immunity in Jawless Vertebrates

The study of immune related genes in lampreys and hagfish provides a unique perspective on the evolutionary genetic underpinnings of adaptive immunity and the evolution of vertebrate genomes. Separated from their jawed cousins at the stem of the vertebrate lineage, these jawless vertebrates have many of the gene families and gene regulatory networks associated with the defining morphological and physiological features of vertebrates. These include genes vital for innate immunity, inflammation, wound healing, protein degradation, and the development, signaling and trafficking of lymphocytes. Jawless vertebrates recognize antigen by using leucine-rich repeat (LRR) based variable lymphocyte receptors (VLRs), which are very different from the immunoglobulin (Ig) based T cell receptor (TCR) and B cell receptor (BCR) used for antigen recognition by jawed vertebrates. The somatically constructed VLR genes are expressed in monoallelic fashion by T-like and B-like lymphocytes. Jawless and jawed vertebrates thus share many of the genes that provide the molecular infrastructure and physiological context for adaptive immune responses, yet use entirely different genes and mechanisms of combinatorial assembly to generate diverse repertoires of antigen recognition receptors.     

Gene doctoring: a method for recombineering in laboratory and pathogenic Escherichia coli strains

Background  

Homologous recombination mediated by the λ-Red genes is a common method for making chromosomal modifications in Escherichia coli. Several protocols have been developed that differ in the mechanisms by which DNA, carrying regions homologous to the chromosome, are delivered into the cell. A common technique is to electroporate linear DNA fragments into cells. Alternatively, DNA fragments are generated in vivo by digestion of a donor plasmid with a nuclease that does not cleave the host genome. In both cases the λ-Red gene products recombine homologous regions carried on the linear DNA fragments with the chromosome. We have successfully used both techniques to generate chromosomal mutations in E. coli K-12 strains. However, we have had limited success with these λ-Red based recombination techniques in pathogenic E. coli strains, which has led us to develop an enhanced protocol for recombineering in such strains.