Tunichrome (TC) is a group of highly reducing, metal-sequestering, low molecular weight compounds possessing two or three catecholate rings attached to a central enamide group that have been isolated from blood cells of several North American ascidian species. We report a modification
of the "free" TC assay that permits a more rapid and convenient aerobic procedure. With this assay a wider range of ascidian species has been surveyed from all suborders and a diversity of geographical locations including Australia. Five Australian phlebobranch species were found
to contain TC in their blood cells, bringing the total to 9 out of 11 species surveyed. Free TC containing three catecholate rings is widely distributed in the suborder Phlebobranchia. Of five stolidobranch species surveyed, one (Molgula manhattensis) contains TC compounds which differ
from phlebobranch TC in having only two catecholate rings. These results show that although free TC is not ubiquitous within the Ascidiacea, it is clear that catechol or catechol derivatives such as dihydroxyphenylalanine are important entities among ascidian blood cell components.
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