Disruption of the single tropomyosin gene in yeast results in the disappearance of actin cables from the cytoskeleton

The yeast tropomyosin gene, designated TPM1, is present in a single copy per haploid genome and encodes a protein with a predicted molecular weight of 23.5 kd. The protein sequence is homologous to higher cell tropomyosins, including the characteristic hydrophobic-hydrophilic pseudoheptapeptide repeats. Indirect immunofluorescence microscopy reveals that tropomyosin is localized with actin cables in wild-type cells. Disruption of TPM1 is not lethal, but results in a reduced growth rate and disappearance of actin cables. Strains carrying the conditional actin mutation act1-2 also lack actin cables; overexpression of tropomyosin in these strains partially restores actin cables. These results strongly suggest that tropomyosin interacts with F actin in vivo and may play an important role in assembling or stabilizing actin cables in yeast.     

Interaction of (Na + K + 2 Cl) cotransport and the Na/K pump in cultured chick cardiac myocytes

We have recently reported the presence of an electroneutral (Na + K + 2 Cl) cotransport mechanism that is bumetanide-sensitive and maintains Cl_i above its electrochemical equilibrium in cultured chick heart cells. In steady state, (Na + K + 2 Cl) cotransport is inwardly directed and so contributes to the Na influx that must be counterbalanced by the activity of the Na/K pump to maintain Na_i homeostasis. We now show that manipulating (Na + K + 2 Cl) cotransport by restoring Cl_o to a Cl-free solution indirectly influences Na/K pump activity because the bumetanide-sensitive recovery of a _infNa ^supi to its control level and the accompanying hyperpolarization could be blocked by 10^–4M ouabain. In another protocol, when the Na/K pump was reactivated by restoring K_o (from 0.5 mM to 5.4 mM) and removing ouabain, the recovery of a_Na was attenuated by 10^–4M bumetanide. The relatively slow rate of ouabain dissociation coupled with the activation of Na influx by (Na + K + 2 Cl) cotransport clearly establishes the interaction of these transport mechanisms in regulating Na_i. Although (Na + K + 2 Cl) cotransport is electroneutral, secondary consequences of its activity can indirectly affect the electrophysiological properties of cardiac cells.     

The effect of oxidants on biomembranes and cellular metabolism

During the reductive process in the tissues, the aerobes generate a number of oxidants. Unless these oxidants are reduced, oxidative damage and cell death would occur. Oxidation of plasma membrane lipids leads to autocatalytic chain reactions which eventually alter the permeability of the cell. The role of oxidative damage in the pathophysiology of diabetic complications and ischemic reperfusion injury of myocardium, especially the changes in the channel activity which may lead to arrhythmia have been studied. Hyperglycemia activates aldose reductase which could efficiently reduce glucose to sorbitol in the presence of NADPH. Since NADPH is also aldose required by glutathione reductase for reducing oxidants, its diversion would lead to membrane lipid oxidation and permeability changes which are probably responsible for diabetic complications such as cataractogenesis, retinopathy, neuropathy etc. Antioxidants such as butylated hydroxy toluene (BHT) and also reductase inhibitors prevent or delay some of these complications. By using patch-clamp technique in isolated frog myocytes, we have shown that hydroxy radicals generated by ferrous sulfate and ascorbate as well as lipid peroxides such as t-butyl hydroperoxide facilitate the entry of Na⁺ by oxidizing Na⁺-channels. Increased intracellular Na⁺ leads to an increase in Na⁺/Ca²⁺ exchange. The increased Na⁺ concentration by itself may produce electrical disturbance which would result in arrhythmia. Increased Ca²⁺ may affect proteases and may help in the conversion of xanthine dehydrogenase to xanthine oxidase, consequently increased production of super oxide radicals. Increased membrane lipid peroxidation and other oxygen free-radical associated membrane damage in myocytes has been demonstrated.     

Diffusion of the Interspecies Electron Carriers H(2) and Formate in Methanogenic Ecosystems and Its Implications in the Measurement of K(m) for H(2) or Formate Uptake

We calculated the potential H(2) and formate diffusion between microbes and found that at H(2) concentrations commonly found in nature, H(2) could not diffuse rapidly enough to dispersed methanogenic cells to account for the rate of methane synthesis but formate could. Our calculations were based on individual organisms dispersed in the medium, as supported by microscopic observations of butyrate-degrading cocultures. We isolated an axenic culture of Syntrophomonas wolfei and cultivated it on butyrate in syntrophic coculture with Methanobacterium formicicum; during growth the H(2) concentration was 63 nM (10.6 Pa). S. wolfei contained formate dehydrogenase activity (as does M. formicicum), which would allow interspecies formate transfer in that coculture. Thus, interspecies formate transfer may be the predominant mechanism of syntrophy. Our diffusion calculations also indicated that H(2) concentration at the cell surface of H(2)-consuming organisms was low but increased to approximately the bulk-fluid concentration at a distance of about 10 mum from the surface. Thus, routine estimation of kinetic parameters would greatly overestimate the K(m) for H(2) or formate.     

Resonance electroconformational coupling: A proposed mechanism for energy and signal transductions by membrane proteins

Recent experiments show that membrane ATPases are capable of absorbing free energy from an applied oscillating electric field and converting it to chemical bond energy of ATP or chemical potential energy of concentration gradients. Presumably these enzymes would also respond to endogenous transmembrane electric fields of similar intensity and waveform. A mechanism is proposed in which energy coupling is achieved via Coulombic interaction of an electric field and the conformational equilibria of an ATPase. Analysis indicates that only an oscillating or fluctuating electric field can be used by an enzyme to drive a chemical reaction away from equilibrium.In vivo, the stationary transmembrane potential of a cell must be modulated to become locally oscillatory if it is to derive energy and signal transduction processes.     

The second stiffest axis of a beam-column: implications for cervical spine trauma

Based on an idealized model of a homogeneous, isotropic beam-column, the second stiffest axis under static loading was derived. The maximum allowable force for the second stiffest axis was then examined. The ratio of the maximum allowable forces of the second stiffest axis to the stiffest axis was established. The stiffness ratio of the second stiffest axis to the stiffest axis was also found. Taking buckling into consideration, the safe load region for all possible acting directions was derived. The implications of the idealized model for cervical spine trauma are discussed.     

mRNAs for two ribosomal proteins are preferentially translated in the chloroplast of Chlamydomonas reinhardtii under conditions of reduced protein synthesis

Previous studies have identified a set of highly phosphorylated proteins of 23–25 kDa accumulated during normal embryogenesis of Zea mays L. and which disappear in early germination. They can be induced precociously in embryos by abscisic acid (ABA) treatment. Here the synthesis and accumulation of this group of proteins and their corresponding mRNAs were examined in ABA-deficient viviparous embryos at different developmental stages whether treated or not with ABA, and in water-stressed leaves of both wild-type and viviparous mutants.During embryogenesis and precocious germination of viviparous embryos the pattern of expression of the 23–25 kDa proteins and mRNAs closely resembles that found in non-mutant embryo development. They are also induced in young viviparous embryos by ABA treatment. In contrast, leaves of ABA-deficient mutants fail to accumulate mRNA in water stress, yet do respond to applied ABA. In water-stressed leaves of wild type plants the mRNAs are induced and translated into 4 proteins with a molecular weight and isoelectric point identical to those found in embryos.These results indicate that the 23–25 kDa protein set is a new member of the recently described class or proteins involved in generalized plant ABA responses.The different pattern of expression for the ABA-regulated 23–25 kDa proteins and mRNAs found in embryo and in vegetative tissues of viviparous mutants is discussed.     

朱鹮(Nipponia nippon)的繁殖习性

文章概述了朱鹮的濒危状况及陕西省洋县1981—1986年的繁殖数量,计6年9窝27幼,已知死亡4只,人工喂养3只。 朱鹮在洋县为留鸟,越冬期间偶尔返回繁殖地,2月中旬后不再离开。有显著的领域性。3月上旬开始营巢,中旬至4月初产卵,多数3枚(1—4枚)。孵卵期30天左右,育雏期约为40天,均由雌雄亲鸟共同承担。6月中下旬全窝育成后一起飞离巢区。     

仙茅属三个国产种的核型研究

本文报道了中国产三种仙茅植物的核型。1.绒叶仙茅Curculigo crassifolia (Baker) Hook. f., 2n=2x=18=10m(4SAT) 8 sm;2.大叶仙茅C.capitulata(Lour.)O. Kuntze,2n=2x=18=10(2SAT) 8sm;3.中华仙茅C.sinensis S.C.Chen,2n=2x=18=8m(3SAT) 10sm(2SAT)。其中中华仙茅的核型为首次报道。虽然三种仙茅的核型都是“2B”型,但中华仙茅的核型不对称性比绒叶仙茅和大叶仙茅强。     

大壁虎的染色体及减数分裂联会复合体的研究

大壁虎(Gekko gecko)的染色体数目为2n=38,核型由2对中着丝粒(Nos.1.4.)、3对亚中着丝粒(Nos.2.3.5)及14对端着丝粒和亚端着丝粒(Nos.6—19)染色体组成。一对核仁组织者(NOR_s),位于第7对端着丝粒染色体的末端。同时,本文还对大壁虎的减数分裂以及联会复合体(S.C)的结构和组型,进行了详细的观察和分析。