title: Reactions between tunichrome Mm-1, a tunicate blood pigment, and vanadium ions in acidic and neutral media.
abstract: Tunichromes are yellow, polyphenolic tripeptides prevalent in blood cells of tunicates (suborders phlebobranchia and stolidobranchia). Spectrophotometric studies of reactions between tunichrome Mm-1 and VV or VIV ions were conducted in vitro in various media to crudely approximate cellular conditions: deionized water, aqueous methanol, and aqueous buffers at pH 2 and 7. Catechol was used in parallel studies for comparison to tunichrome and was found to be a good model for tunichrome reactivity. For VIV in pH 7 buffer, both catechol and Mm-1 formed complexes with VIV ions, and no redox products were found. For VV in pH 2 buffer, both catechol and Mm-1 were oxidized by VV ions. Room temperature EPR qualitatively showed that Mm-1 in pH 2 buffer reduced VV ions to free VIV ions. For VV in pH 7 buffer, Mm-1 was oxidized by VV ions and formed VIV complexes. At higher concentrations, the VIV complexes were observed by low temperature EPR [Grant, K. B. (1994) Dissertation, Columbia University; Grant, K. B., et al. (1996) J. Inorg. Biochem. (manuscript in preparation)]. Using a colorimetric assay for VIII, we found that reactions between Mm-1 and VV or VIV ions in pH 7 buffer clearly did not generate appreciable quantities of VIII products. Thus, the colorimetric VIII assay resolved the issue of VIII product formation raised in EPR studies of Mm-1 [cf. Ryan, D. E., et al. (1992) Biochemistry 35, 8651-8661]. Overall, the results provide insights into tunichrome-vanadium chemistry and identify conditions which promote complexation and/or redox reactions in vitro.
authors.affiliation: Department of Chemistry, Columbia University, New York, New York 10027, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Ryan
authors.forename: K B
authors.initials: KB
authors.lastname: Grant
authors.forename: K
authors.initials: K
authors.lastname: Nakanishi
mesh_terms: D000818:Animals; D002151:Calorimetry; D002396:Catechols / Q000737:chemistry; D002412:Cations; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D009930:Organic Chemicals; D010860:Pigments, Biological / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D014561:Urochordata; D014639:Vanadium / Q000737:chemistry*
chemical_list: D002396:Catechols; D002412:Cations; D009930:Organic Chemicals; D010860:Pigments, Biological; D014639:Vanadium; C021765:tunichrome; C034221:catechol