A new scanilepiform from the Lower Triassic of northern Gansu Province,China, and phylogenetic relationships of non‐teleostean Actinopterygii

A new scanilepiform, Beishanichthys brevicaudalis gen. et sp. nov. , is named and described based on fossils from the Lower Triassic lake deposits exposed in Beishan area, Gansu Province, China. The discovery documents a new record of this group, which is significantly older than other known scanilepiforms from China, and is slightly younger than Evenkia from the Lowest Triassic of Central Siberia. Although the Beishan beds were previously interpreted as Late Permian in age, based on megaplant fossils, this new discovery supports the reinterpretation of the deposits as Early Triassic in age, based on vertebrate fossils from the same locality and horizon. Phylogenetic analysis was conducted to resolve the relationships of Scanilepiformes with other actinopterygian clades, and the inter‐relationships within Scanilepiformes. Contrary to previous thought that scanilepiforms are closely related to the Amiidae, the phylogenetic results of this study recognize the Scanilepiformes as stem‐group neopterygians. Relationships of the Scanilepiformes and Australosomus with other neopterygians remain unresolved. With a characteristic long‐based dorsal fin, scanilepiforms represent a small group that emerged in Early Triassic freshwater environments, inhabited Eurasia and North America during the Middle–Late Triassic, briefly invaded the marine environment by the Late Triassic in Europe, and became extinct at the end of Triassic. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 595–612.     

Pheromone deactivation catalyzed by receptor molecules: a quantitative kinetic model

A quantitative model of pheromone-receptor interaction and pheromone deactivation, the supposed rate-limiting processes underlying the receptor potential kinetics, is worked out for the moth Antheraea polyphemus. In this model, the pheromone interacts with the receptor molecule while bound to the reduced form of the pheromone binding protein. The receptor molecules--besides their receptor function-- catalyze the observed shift of the pheromone-binding protein from the reduced to the oxidized form (Ziegelberger, G., Eur. J. Biochem., 232, 706-711, 1995), which deactivates the pheromone bound to pheromone binding protein. With the following parameters, the model fits morphological, radiometric, electrophysiological and biochemical data: a maximum estimate of 1.7 x 10(7) receptor molecules/cell (with 40,000 units/micron 2 of receptor cell membrane), rate constants k1 = 0.2/(s.microM) for the association, k2 = 10/s for the dissociation of the ternary complex of binding protein, pheromone and receptor, and k3 = 10/s for the deactivation via the redox shift. With these parameters, the duration of elementary receptor potentials elicited by single pheromone molecules (approximately 50 ms) reflects the lifetime of the ternary complex, tau = 1/(k2 + k3). The receptor occupancy produced by the model for threshold stimuli fits the sensitivity of the receptor cell to single pheromone molecules.      

Using a logical model to predict the growth of yeast

Background  

A logical model of the known metabolic processes in S. cerevisiae was constructed from iFF708, an existing Flux Balance Analysis (FBA) model, and augmented with information from the KEGG online pathway database. The use of predicate logic as the knowledge representation for modelling enables an explicit representation of the structure of the metabolic network, and enables logical inference techniques to be used for model identification/improvement.     

Flux detectors versus concentration detectors: two types of chemoreceptors

Dose-response curves relating the external stimulus concentration to receptor occupancy differ in two types of chemoreceptor organs. In 'concentration detectors' the receptor molecules at the receptor cell membrane are directly exposed to the external stimulus concentration; these organs exhibit the well-known hyperbolic dose-response relationship reflecting the association-dissociation of stimulus and receptor molecules. In contrast, 'flux detectors' accumulate the stimulus molecules in a perireceptor compartment. In flux detectors, deactivation of stimulus molecules may be in balance with arrival, as a prerequisite for producing a constant effective stimulus concentration at constant adsorptive flux of stimulus molecules. In a simple model of a flux detector in which receptor molecules themselves catalyze the deactivation, the dose-response relationship is linear. It reflects the rate of stimulus deactivation. If the deactivation is catalyzed by a separate enzyme, the dose-response relationship can be close to hyperbolic, or linear. In all cases, the receptor molecules are maximally occupied if the adsorptive flux equals or exceeds the maximum rate of stimulus deactivation. The time course of the receptor potential recorded from moths' pheromone receptors depends on the odor compound, which suggests that a peripheral process, possibly the stimulus deactivation, is the slowest, rate-limiting process of the transduction cascade. Further evidence comes from experiments with stimuli oversaturating the mechanism responsible for the decline of the receptor potential.