日本財団 図書館


OST-10B: Marine Physiology and Natural Products
ACCUMULATION AND REDUCTION OF VANADIUM BY ASCIDIANS
Hitoshi Michibata
 
Marine Biological Laboratory, Graduate School of Science Hiroshima University, Mukaishima-cho, Hiroshima, JAPAN
hmichi@sci.hiroshima-u.ac.jp
 
Ascidians, so-called sea squirts, are known to accumulate high levels of vanadium. The highest concentration of vanadium, 350 mM, was found in the blood cells of Ascidia gemmata belonging to the suborder Phlebobranchia. This concentration is 107 times higher than that in seawater. Vanadium accumulated in the blood cells is reduced to V(III) via V(IV) and stored in vacuoles of vanadocytes (vanadium-containing blood cells). The contents of vacuoles are maintained in an extremely low pH of 1.9 by vacuolar-type H+-ATPase.
 
Recently, we have found out at least two types of vanadium-binding protein, 12.5 kDa and 15 kDa, and cloned cDNAS encoding them. Both novel proteins, designated as Vanabins, have been disclosed to consist of about 120 amino acids in which the content of cysteine residues is very high and occurrenee of cysteine residues at regular intervals is characteristic and common in both novel proteins. Recombinant Vanabin was found to bind about 10 to 20 atoms of vanadium and its binding constant is 10-6 to 10-7M, which might have a clue to resolve the mechanism of vanadium accumulation. Concerning the reduction of vanadium in vanadocytes, we have localized four enzymes involved in the pentose phosphate pathway that is known to produce a reducing agent, NADPH. In fact, NADPH was revealed to conjugate the reduction of V(V) to V(IV) in vitro. Furthermore, the other types of protein such as a metal-ATPase and cDNAc involved in the accumulation and reduction of vanadium will be re ported.
 
OST-10B: Marine Physiology and Natural Products
BIOLOGICAL ACTIVITIES OF MULTIPLE LECTINS FROM THE TOXOPNEUSTID SEA URCHINS
Hideyuki Nakagawa1, Fumihiko Satoh1, Hitomi Sakai1, Hiromi Hayashi1 and Yasuhiro Ozeki2
 
1Department of Life Sciences, University of Tokushima, Tokushima, JAPAN
sea-hide@ias.tokushima-u.ac.jp
 
2Department of System Element, Yokohama City University Yokohama, JAPAN
 
The toxopneustid sea urchins, Toxopneustes pileolus and Tripneustes gratilla have well-developed globiferous pedicellariae with bioactive substances. Two D-galactose-binding lectins (SUL-I and SUL-II) and a heparin-binding lectin (TGL-I) were purified from T. pileolus and T. gratilla using gel filtration chromatography, affinity chromatography, and reverse-phase HPLC. SUL-I and SUL-II from the large flower-like globiferous pedicellariae of T. pileolus are D-galactose-binding proteins with molecular masses of 32 kDa and 23 kDa, respectively. On the other hand, TGL-I from the globiferous pedicellariae of T. gratilla is a Ca2+-independent heparin-binding protein with a molecular mass of 23 kDa. SUL-I induced mitogenic stimulation on murine splenocytes but SUL-II and TGL-1 did not. At higher dose ranges SUL-1 had weak cytotoxic activity on murine P388 leukemic cells. Furthermore, SUL-I promoted chemotaxis of human polymorphonuclear leukocytes and monocytes.
 
Sequence analysis of intact SUL-I revealed the N-terminal sequence from Ala-1 to Ile-35. The partial amino acid sequence of SUL-I is related to SUEL, a D-galactose-specific lectin from the eggs of sea urchin Anthrocidaris crassispina. Moreover, SUL-I showed sequence homology to the segment Tyr-Gly-Arg of the D-rhamnose-binding lectins (SAL and STL2) from fish eggs.
 
Although the physiological roles of SUL-I, SUL-II and TGL-I are not clear, the primary role of pedicellarial lectins may be defense against a foreign body. The present results suggest an extracellular function for SUL-I that may have wide-ranging effects, and suggest that the toxopneustid sea urchins might be a resource for biologically active substances with an interesting mechanism of action.
 
OST-10B: Marine Physiology and Natural Products
OPTIMAL SALINITY CULTURE CONDITIONS FOR SEA BREAM GROWTH: INFERENCES FROM HORMONAL STATUS AND IMMUNE FUNCTION
Norman Y.S. Woo and Eddie E. Deane
 
Department of Biology, The Chinese University of Hong Kong Hong Kong, CHINA
normanwoo@cuhk.edu.hk
 
Establishing the optimal culture conditions for fish culture is complex and the interaction between environmental salinity, hormones and immune function needs to be considered. Using the euryhaline sea bream as our experimental animal and culture tanks equipped with water recirculation we have been able to test a range of salinities [hypersaline (50ppt), seawater (33ppt), isoosomotic (12ppt) and hypoosmotic (6ppt)] in order to establish which is the most beneficial for sea bream growth and health. From our experiments we have demonstrated that sea bream display a considerable degree of euryhalinity, being able to maintain homeostasis with unaltered plasma ions (Na+, Ca+ and Cl-) and muscle moisture for chronic periods of acclimation in all salinities. Since the circulating levels of corticosteroids and thyroid hormones may play an important role in regulating both catabolic and anabolic processes we have measured the serum levels of cortisol, thyroxine (T4) and tri-iodothyronine (T3) in salinity acclimated sea bream and found that both cortisol and T4 were at lowest levels in isoosmotic groups whereas serum T3 remained unaltered in all salinity groups. In terms of growth related responses, the mRNA levels of hepatic insulin-like growth factor-I (IGF-I) and glucose-6-phosphate dehydrogenase (G6PDH) were studied and it was found that both were significantly highest in isoosmotic acclimated sea bream. Since the levels of hepatic IGF-I provides for an assessment as to the status of the growth hormone (GH) - IGF-I axis and the levels of G6PDH indicate the status of the pentose phosphate pathway, we can conclude that both the GH-IGF-I axis and the pentose phosphate pathway are upregulated in isoosmotic adapted sea bream. The non-specific immune response of salinity acclimated sea bream was assessed using an in vitro assay for determination of macrophage phagocyiosis and it was found that phagocytic activity was highest in macrophages taken from isoosmotic acclimaied fish. Since we have previously determined that GH and cortisol stimulate and suppress macrophage phagocyiosis respectively then there does appear to be a relationship between environmental salinity, hormones and immune function. From the data obtained in this study it would appear that isoosmotic culture conditions are beneficial for sea bream growth.
 
This work was supported by Hong Kong Research Grants Council Earmarked Grants (CUHK 4135/98M, CUHK4168/99M, CUHK4252/00M, CUHK4146/01M) awarded to NYSW.







日本財団図書館は、日本財団が運営しています。

  • 日本財団 THE NIPPON FOUNDATION