Carbamoyl phosphate synthetase: a tunnel runs through it

The direct transfer of metabolites from one protein to another in a biochemical pathway or between one active site and another within a single enzyme has been described as substrate channeling. The first structural visualization of such a phenomenon was provided by the X-ray crystallographic analysis of tryptophan synthase, in which a tunnel of approximately 25 Å in length was observed. The recently determined three-dimensional structure of carbamoyl phosphate synthetase sets a new long distance record in that the three active sites are separated by nearly 100 Å.     

Aminoacyl-tRNA synthetases

Crystallographic studies of a number of aminoacyl-tRNA synthetases and their complexes with ATP, amino acid and cognate tRNA are leading to an increasingly detailed picture of how these sophisticated enzymes function. Within the two distinct structural classes of ten synthetases, many common features are apparent, although evolution has led to many interesting idiosyncrasies in certain enzymes. Recent advances, specially concerning class II enzymes, have increased out knowledge of both the role of electrophiles in the mechanism of amino acid activation and cross-subunit tRNA recognition and help solve the evolutionary puzzles that have emerged from the extension of the aminoacyl-tRNA synthetase database to include Archae     

Progress towards synthetic enzymes for phosphoester hydrolysis

Synthesis of artificial enzymes for catalyzing phosphoester hydrolysis has been attracting interest for a long time. The remarkable discovery that lanthanide ions catalyze the hydrolysis of DNA and RNA spurred the trend. Currently, progress is being made, mainly in the preparation of homogeneous catalysts, the promotion of catalytic activity by using acid/base cooperation within catalysts, the detailed understanding of the reaction mechanisms involved, and the design of artificial enzymes expressing high specificity and catalytic turn-over.     

Solid-phase oligosaccharide synthesis and related technologies

Research efforts directed at the development of methodologies effective for solid-phase synthesis of oligosaccharides have resulted in a number of impressive achievements. In addition, closely related technologies, such as soluble polymer-supported synthesis and fluorous synthesis of the same class of molecules, have proved to be quite promising.     

Protein-biotin interactions

The three-dimensional structures of several biotin-binding proteins are now known, giving insights into the molecular architecture of the binding sites for biotin. In combination with biochemical and computational approaches, these structural insights provide the basis for our present understanding of biotin—protein interactions which, in some cases, give rise to spectacular binding constants.     

Heterocyst formation in Anabaena

Heterocystous cyanobacteria grow as multicellular organisms with a distinct one-dimensional developmental pattern of single nitrogen-fixing heterocysts separated by approximately ten vegetative cells. Several genes have been identified that are required for heterocyst development and pattern formation. A key regulator, HetR, has been recently shown to be aserine-type protease.     

离子对反相HPLC测定人红细胞PRPP合成酶活性

红细胞PRPP合成酶是红细胞内核苷酸代谢的关键酶,它参与嘌呤核苷酸的从头合成与补救合成途径,催化ATP与5-磷酸核糖（R5P）反应生成PRPP与AMP,而PRPP则是嘌呤嘧啶核苷酸合成途径的一个关键性中间产物．Stocchi等[1]采用离子对反相高效液相色谱法（IPrHPLC）测定红细胞内ATP,ADP．AMP含量,曾获得满意的谱峰分离效果．Sakuma等[2]应用rHPLC法测定了正常人及痛风等患者红细胞的PRPP合成酶活性,我们将Sakuma等的测酶技术与IPrHPLC法相结合,改用单液等度洗脱,达到了操作简便和灵敏、准确的要求．1材料和方法1．1试剂…     

A role for the cerebellum in the control of limb movement velocity

Accepting, rejecting or modifying the many different theories of the cerebellum's role in the control of movement requires an understanding of the signals encoded in the discharge of cerebellar neurons and how those signals are transformed by the cerebellar circuitry. Particularly challenging is understanding the sensory and motor signals carried by the two types of action potentials generated by cerebellar Purkinje cells, the simple spikes and complex spikes. Advances have been made in understanding this signal processing in the context of voluntary arm movements. Recent evidence suggests that mossy fiber afferents to the cerebellar cortex are a source of kinematic signals, providing information about movement direction and speed. In turn, the simple spike discharge of Purkinje cells integrates this mossy fiber information to generate a movement velocity signal. Complex spikes may signal errors in movement velocity. It is proposed that the cerebellum uses the signals carried by the simple and complex spike discharges to control movement velocity for both step and tracking arm movements.     

Do we understand the evolution of genomic imprinting?

The conflict theory is the only hypothesis to have attracted any critical attention for the evolution of genomic imprinting. Although the earliest data appeared supportive, recent systematic analyses have not confirmed the model's predictions. The status of theory remains undecided, however, as post-hoc explanation can be provided as to why these predictions are not borne out.     

Inertial vestibular coding of motion: concepts and evidence

Central processing of inertial sensory information about head attitude and motion in space is crucial for motor control. Vestibular signals are coded relative to a non-inertial system, the head, that is virtually continuously in motion. Evidence for transformation of vestibular signals from head-fixed sensory coordinates to gravity-centered coordinates have been provided by studies of the vestibulo-ocular reflex. The underlying central processing depends on otolith afferent information that needs to be resolved in terms of head translation related inertial forces and head attitude dependent pull of gravity. Theoretical solutions have been suggested, but experimental evidence is still scarce. It appears, along these lines, that gaze control systems are intimately linked to motor control of head attitude and posture.     

Antifreeze proteins

Antifreeze proteins comprise a structurally diverse class of proteins that inhibit the growth of ice. Recently, new AFP types have been discovered; more active AFPs have been isolated; antecedents have been recognized supporting the notion of recent, multiple origins; and detailed structures have emerged leading to models for their adsorption to ice     

The chemical-biological interface: developments in automated and miniaturised screening technology

The rapidly changing developments in genomics and combinatorial chemistry, generating new drug targets and large numbers of compounds, have caused a revolution in high-throughput screening technologies. Key to this revolution has been the introduction of robotics and automation, together with new biological assay technologies (e.g., homogeneous time resolved fluorescence). With ever increasing workloads, together with economic and logistical constraints, miniaturisation is rapidly becoming essential for the future of high-throughput screening and combinatorial chemistry. This is evident from the introduction of high-density microtitre plates, small volume liquid handling robots and associated detection technology.     

Infection-related development in the rice blast fungus Magnaporthe grisea

Recent developments have been made in the identification of signal transduction pathways and gene products involved in the infection-related development of the rice blast fungus, Magnaporthe grisea. It has been established that cAMP-dependent and MAP kinase-mediated signaling are both critical for appressorium morphogenesis and function. These signaling pathways may act downstream of hydrophobin-mediated surface sensing by the growing germ tube. Several genes have been identified that are required for invasive growth of M. grisea including genes that allow adaptation of fungal metabolism to growth within plant tissues.     

New structures of allosteric proteins revealing remarkable conformational changes

New three-dimensional structures of allosteric proteins reveal they have a flexible architecture that is instrumental to the regulation of protein function. Highlights are the structures of GroEL, pyruvate kinase, -3-phosphoglycerate dehydrogenase and the acetylcholine receptor. Furthermore, significant progress in understanding the nature of the intermediates involved in an allosteric reaction has been achieved through recent spectroscopic and crystallographic studies on haemoglobin.     

Sister chromatid cohesion in mitosis

Sister chromatid cohesion is essential for accurate chromosome segregation during the cell cycle. Newly identified structural proteins are required for sister chromatid cohesion and there may be a link in some organisms between the processes of cohesion and condensation. Proteins that induce and regulate the separation of sister chromatids have also been recently identified.     

Three-dimensional structural studies on fragments of fibrinogen and fibrin

Fibrinogen is a 340 kDa glycoprotein found in the blood plasma of all vertebrates. It is transformed into a fibrin clot by the action of thrombin. Recent X-ray structures of core fragments of both fibrinogen and fibrin have revealed many details about this polymerization event. These include structures of a 30 kDa recombinant γC domain, an 86 kDa fragment D from human fibrinogen and a cross-linked double-D fragment from fibrin.     

Reproductive isolation in Drosophila: how close are we to untangling the genetics of speciation?

Our understanding of the genetic basis of reproductive isolation in Drosophila has progressed rapidly over the past decade. Details of the genetic structure of hybrid sterility have been revealed and a general consensus has been reached concerning the genetic bases of Haldane's rule. Genetic analyses now reach beyond hybrid sterility and inviability, allowing us to make important comparisons across different traits involved in reproductive isolation. Expansion of genetic studies to include rescue of hybrid incompatibilities has opened the door for more detailed molecular and developmental analyses of reproductive isolation than has ever before been possible.     

Population coding and behavioral choice

Many individual behavioral acts are produced by the combined activity of large populations of broadly tuned neurons, and the neuronal populations for different behaviors can overlap. Recent experiments monitoring and manipulating neuronal activity during behavioral decisions have begun to shed light on the mechanisms that enable overlapping populations of neurons to generate choices between categorically distinct behaviors.     

Out of Africa? What do genes tell us?

Genetic diversity patterns in nuclear versus mitochondrial systems and in low versus high mutation rate systems do not support the hypothesis of a recent African origin for all of humanity following a split between Africans and non-Africans 100,000 years ago, nor do genetic distance data. Geographical analyses of nuclear and mitochondrial gene trees do not support the hypothesis of a recent global replacement of humans coming out of Africa, although a local replacement event in Europe is indicated by these analyses and recent studies on Neandertal DNA. The gene tree analyses instead indicate that genetic interchanges have ensured that all of humanity has evolved as a single evolutionary lineage with no major splits.