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

Vanadium K-edge x-ray absorption spectroscopy (XAS) was used to examin e whole blood preparations from the tunicates Ascidia nigra and Ascidi a ceratodes, Each XAS spectrum exhibits a rising edge inflection near 5480 eV characteristic of vanadium(III) and an intensity maximum at 54 84.0 eV. In A. ceratodes blood cells, intrinsic aquo-VSO4+ complex ion is indicated by an inflection feature at 5476 eV in the first derivat ive of the vanadium It-edge XAS spectrum, but this feature is notably absent from the first derivative of the vanadium It-edge spectrum of b lood 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 b lood cells, implying that vanadyl ion represents similar to 25% of the endogenous vanadium, However, the energy position of the rising edge inflection of the vanadium It-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 c ontrast to A. ceratodes, a significant fraction of the blood cell vana dium(III) in A. nigra is apparently in a ligation environment substant ially different from that provided by water. These novel species-relat ed differences may have taxonomic significance.