VANADIUM IN ASCIDIANS - CHANGES IN VANADIUM COORDINATION AND OXIDATION-STATE UPON CELL-LYSIS

Changes in vanadium coordination during cell lysis have been followed by EPR spectroscopy of the blood cells of the phlebobranch ascidians A scidia ceratodes and Phallusia julinea. The spectra obtained for A. ce ratodes whole blood samples can be mainly ascribed to aquated oxovanad ium(IV) in which the signals are broadened in freshly frozen blood rel ative to when the cells are lysed by thawing. The sources of this broa dening are discussed and it is shown that the oxovanadium(IV) signal h as its origin in a small percentage of damaged or lysed cells which re lease vanadium into a low sulfate, low acid environment in fresh sampl es. When thawed, the cells lyse releasing acid and sulfate into the en vironment of the oxovanadium(IV), with consequent narrowing of the EPR spectral linewidth. Freshly frozen P. julinea blood cell samples have EPR spectra with parameters intermediate between aquated oxovanadium( IV) and the ''type I'' parameters observed in a previous investigation of tissue samples of this species (S. G. Brand, C. J. Hawkins, A. T. Marshall, G. W. Nette, and D. L. Pany, Comp. Biochem. Physiol. 93B, 42 5 (1989)). A. ceratodes tissue samples also have EPR spectra that diff er from that of the blood. It is suggested that EPR studies on tissue samples are more indicative of the resting state of vanadium in the ce lls as there is more physiological material to provide a pH buffering effect to stabilize the cells. Schemes are presented which incorporate all of the EPR observations in ascidian literature, where cellular ly sis is proposed to be accompanied by vanadium undergoing oxidation and a series of chelate exchanges from a ''type I'' complex to aquated ox ovanadium(IV). Protons released during these exchanges are suggested t o provide the acidity characteristic of blood cell lysates. The biolog ical implications of the concomitant release of vanadium and tunichrom e (S. W. Taylor, D. L. Parry, C. J. Hawkins, and J. H. Swinehart, Comp . Biochem. Physiol. 106A, 531 (1993)) from the blood cells, to the pro cess of wound repair are discussed.