title: Vanadium K-edge x-ray absorption spectroscopy reveals species differences within the same ascidian genera. A comparison of whole blood from Ascidia nigra and Ascidia ceratodes.
abstract: Vanadium K-edge x-ray absorption spectroscopy (XAS) was used to examine whole blood preparations from the tunicates Ascidia nigra and Ascidia ceratodes. Each XAS spectrum exhibits a rising edge inflection near 5480 eV characteristic of vanadium(III) and an intensity maximum at 5484.0 eV. In A. ceratodes blood cells, intrinsic aquo-VSO4+ complex ion is indicated by an inflection feature at 5476 eV in the first derivative of the vanadium K-edge XAS spectrum, but this feature is notably absent from the first derivative of the vanadium K-edge spectrum of blood cells from A. nigra. A strong pre-edge feature at 5468.6 eV also uniquely distinguishes the vanadium K-edge XAS spectrum of A. nigra blood cells, implying that vanadyl ion represents approximately 25% of the endogenous vanadium. However, the energy position of the rising edge inflection of the vanadium K-edge XAS spectrum of A. nigra (5479.5 eV) is 1 eV lower than that of A. ceratodes (5480.5 eV), the reverse of any expected shift arising from the endogenous vanadyl ion. Thus, in contrast to A. ceratodes, a significant fraction of the blood cell vanadium(III) in A. nigra is apparently in a ligation environment substantially different from that provided by water. These novel species-related differences may have taxonomic significance.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
authors.forename: P
authors.initials: P
authors.lastname: Frank
authors.forename: K O
authors.initials: KO
authors.lastname: Hodgson
authors.forename: K
authors.initials: K
authors.lastname: Kustin
authors.forename: W E
authors.initials: WE
authors.lastname: Robinson
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000818:Animals; D013045:Species Specificity; D014561:Urochordata / Q000502:physiology*; D014639:Vanadium / Q000378:metabolism*; D017968:Vanadium Compounds / Q000378:metabolism*
chemical_list: D017968:Vanadium Compounds; D014639:Vanadium