The quaternary structure of four crustacean two-hexameric hemocyanins: immunocorrelation,stoichiometry, reassembly and topology of individual subunits

Summary Two-hexameric (2×6) hemocyanins from the brachyuran crabsCancer pagurus andCallinectes sapidus, the freshwater crayfishAstacus leptodactylus and the lobsterHomarus americanus were isolated and dissociated into native subunits.The subunits of each hemocyanin were analyzed by electrophoresis and immunology. Three immunologically distinct subunit types, which were termed, and, could be identified in each case. They were isolated preparatively, and interspecifically correlated. Subunit is subdivided into several electrophoretically distinct isoforms which are immunologically closely related (Astacus) or identical (other species). InAstacus andCancer one of these isoforms was shown to dimerize and to act as inter-hexamer bridge. It represents a fourth subunit type termed. A fifth, diffuse component, which in PAGE migrated at the position of a dimer, was identified in the crossed immunoelectrophoretic patterns as denatured hemocyanin.A common feature of the four hemocyanins is the presence of 4 copies of and 8 copies of/ within the 2×6 particles. The: ratio is 4:4 in the two Astacidea and 6:2 in the two Brachyura. exists in 2 copies inAstacus andCancer which means that a single dimer- is present in a two-hexamer. This leaves 2 monomeric copies inAstacus and 4 inCancer.Every subunit from the four species except ofAstacus - was capable to form hexamers in reassembly experiments. If subunit combinations were tested, hetero-hexamers were formed preferentially. Two-hexamers were reconstituted only in the presence of all subunit types and the native subunit stoichiometry was required to obtain twohexamers in considerable yields. Factors limiting 2×6 reassembly are discussed.Authentic 2×6 molecules ofAstacus, Homarus andCancer hemocyanin were immunolabeled with subunit-specific antibody fragments (F_ab) or IgG molecules, and the resulting immuno complexes were studied in the electron microscope. A topological model of the quaternary structure of decapod 2×6 hemocyanins is derived, showing the position of each copy of the four subunit types. In this model, the inter-hexamer bridge- is surrounded by two and two subunits forming the central core of the dodecamer. Two additional and two additional subunits form the periphery together with one subunit occupying the peripheral short edges of each hexameric half structure. The model is discussed with respect to the current literature.Abbreviations PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate This paper is decicated to Professor Dr. Bernt LinzenPreliminary accounts of this work have been presented in the proceedings of a symposium at Tutzing 1985. Linzen B (ed) (1986) Invertebrate oxygen carriers. Springer, Berlin Heidelberg New York. This also includes: Stöcker et al. 1986; Markl et al. 1986) and in a review article (Markl 1986)     

Wave propagation in cardiac tissue and effects of intracellular calcium dynamics (computer simulation study)

Computer simulation using Luo-Rudy I1 model of ventricular myocyte showed that intracellular calcium dynamics become irregular in case of high rate stimulation. This causes the transition from stationary to nonstationary spiral wave and its breakup in 2D model of cardiac tissue. Obtained results suggest how ventricular fibrillation may occur due to the abnormalities of intracellular calcium dynamics. The short review of existing cardiac cell models with calcium dynamics is presented.     

The future of ecolabels

The International Journal of Life Cycle Assessment -     

A rapid ceramide synthase activity using NBD-sphinganine and solid phase extraction

Ceramides are synthesized by six mammalian ceramide synthases (CerSs), each of which uses fatty acyl-CoAs of different chain lengths for N-acylation of the sphingoid long-chain base. We now describe a rapid and reliable CerS assay that uses a fluorescent N-[6-[(7-nitrobenzo-2-oxa-1,3-diazol-4-yl) (NBD) sphinganine substrate followed by separation of the NBD-lipid substrate and products using solid phase extraction (SPE) C18 chromatography. SPE chromatography is a quick and reliable alternative to TLC, and moreover, there is no degradation of either NBD-sphinganine or NBD-ceramide. We have optimized the assay for use with minimal amounts of protein in a minimal volume. This assay will prove useful for the analysis of CerS activity, which is of particular importance in light of the growing involvement of CerS in cell regulation and in the pathology of human diseases.     

Testing the stages model in the adaptive radiation of cichlid fishes in East African Lake Tanganyika

Adaptive radiation (AR) is a key process in the origin of organismal diversity. However, the evolution of trait disparity in connection with ecological specialization is still poorly understood. Available models for vertebrate ARs predict that diversification occurs in the form of temporal stages driven by different selective forces. Here, we investigate the AR of cichlid fishes in East African Lake Tanganyika and use macroevolutionary model fitting to evaluate whether diversification happened in temporal stages. Six trait complexes, for which we also provide evidence of their adaptiveness, are analysed with comparative methods: body shape, pharyngeal jaw shape, gill raker traits, gut length, brain weight and body coloration. Overall, we do not find strong evidence for the ‘stages model’ of AR. However, our results suggest that trophic traits diversify earlier than traits implicated in macrohabitat adaptation and that sexual communication traits (i.e. coloration) diversify late in the radiation.