No abstract

SUMMARY The dermis of sea cucumbers is a catch connective tissue or mutable connective tissue that exhibits large changes in mechanical properties. A stiffening protein, tensilin, has been isolated from the sea cucumber Cucumaria frondosa. We purified a similar protein, H-tensilin, from Holothuria leucospilota, which belongs to a different family to C. frondosa. H-tensilin appeared as a single band with an apparent molecular mass of 34 kDa on SDS-PAGE. No sugar chain was detected. Tryptic fragments of the protein had homology to known tensilin. H-tensilin aggregated isolated collagen fibrils in vitro in a buffer containing 0.5 mol l–1 NaCl with or without 10 mmol l–1 Ca2+. The activity of H-tensilin was quantitatively studied by dynamic mechanical tests on the isolated dermis. H-tensilin increased stiffness of the dermis in the soft state, induced by Ca2+-free artificial seawater, to a level comparable to that of the standard state, which was the state found in the dermis rested in artificial seawater with normal ionic condition. H-tensilin decreased the energy dissipation ratio of the soft dermis to a level comparable to that of the standard state. When H-tensilin was applied on the dermis in the standard state, it did not alter stiffness nor dissipation ratio. The subsequent application of artificial seawater in which the potassium concentration was raised to 100 mmol l–1increased stiffness by one order of magnitude. These findings suggest that H-tensilin is involved in the changes from the soft state to the standard state and that some stiffening factors other than tensilin are necessary for the changes from the standard to the stiff state.

Twenty-two samples of allanite-(Ce) taken from granitic rocks in Japan have been characterized by electron-microprobe analysis. In back-scattered-electron (BSE) images, the allanite-(Ce) is homogeneous or characterized by various types of zoning features: oscillatory, normal or irregular types. Thirteen samples contain appreciable amounts of Mn (0.14-D.59 apfu). The Mnrich crystals (2-6 cm long) are larger than the crystals of Mn-poor allanite-(Ce) (0.5-2 cm long). Samples of the two groups differ considerably from each other in chondrite-normalized REE patterns: Mn-poor allanite-(Ce) is relatively rich in LREE, as is common in igneous allanite, whereas the Mn-ricli allanite-(Ce) exhibits an enrichment in the middle rare-earth elements (MREE). The relationship between Mn-rich and Mn-poor allanite-(Ce) is expressed by the coupled substitution Mn2+ + (MREE, HREEP+~Ca2+ + LREE3+. The presence of Mn-rich allanite-(Ce) in the Japanese island arc, in conjunction with occurrences of Mn-rich and REE-bearing epidote-group minerals in manganese deposits, support a link with subduction-zone processes. The granitic rocks containing Mn-poor allanite-(Ce) belong to the magnetite-series granitic rocks, whereas those containing Mn-rich allanite-(Ce) correspond to the ilmenite series, and seem to have formed from a volatile-enriched magma. Therefore, the Mn content in allanite-(Ce) contains petrogenetic information.

The chemical compositions of cavansite and pentagonite, in which H 2 O contents and vanadium (in an unknown oxidation state) are present, were determined by thermogravimetry -differential thermal analysis (TG -DTA), electron spin resonance (ESR), and electron microprobe analysis (EMPA). Furthermore, the mechanism of dehydration of the minerals and presence of the hydrous species such as H 2 O, H 3 O + , and OH − in the aforementioned minerals have been investigated by TG -DTA, high -temperature X -ray diffraction (HT -XRPD) analysis, Fourier -transform infrared (FTIR) spectroscopy, and single -crystal XRD analysis. The results of TG -DTA and HT -XRD revealed that no reversible transitions occur between cavansite and pentagonite when they are heated in air and that no intermediate amorphous phase exists in these two minerals. Gradual dehydration of cavansite in the temperature range of 225 -550 °C was attributed to the removal of both oxonium (H 3 O + ) and hydroxyl ions (OH − ); the IR absorption bands of cavansite observed at 3186 and 3653 cm −1 were assigned to H 3 O + and OH − stretching vibrations, respectively. Moreover, the exact distribution of hydrogens in the crystal structure of the cavansite refined in this study was determined by applying the valence -matching principle; the results showed the existence of H 3 O + and OH − . Thus, the structural formula of cavansite should be revised to Ca(VO)(Si 4 O 10 )·(H 2 O) 4−2x (H 3 O) x (OH) x , in contrast to that of pentagonite, Ca(VO)(Si 4 O 10 )·4H 2 O. The changes in the ion product constant of water with temperature and pressure suggest that pentagonite is formed when the hydrothermal fluid is in supercritical condition (>300 °C), while cavansite is formed when the hydrothermal fluid is not in supercritical condition. Thus, cavansite is identified as a low -temperature form and pentagonite as a high -temperature one.