Reactions between Tunichrome Mm-1, a Tunicate Blood Pigment, and Vanadium Ions in Acidic and Neutral Media

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• 作者：Daniel E. Ryan ; Kathryn B. Grant ; and Koji Nakanishi
• 刊名：Biochemistry
• 出版年：1996
• 出版时间：July 2, 1996
• 年：1996
• 卷：35
• 期：26
• 页码：8640 - 8650
• 全文大小：399K
• 年卷期：v.35,no.26(July 2, 1996)
• ISSN：1520-4995

文摘

Tunichromes are yellow, polyphenolic tripeptides prevalent inblood cells of tunicates (subordersphlebobranchia and stolidobranchia). Spectrophotometric studies ofreactions between tunichrome Mm-1and V^V or V^IV ions were conducted invitro in various media to crudely approximate cellularconditions:deionized water, aqueous methanol, and aqueous buffers at pH 2 and 7.Catechol was used in parallelstudies for comparison to tunichrome and was found to be a good modelfor tunichrome reactivity. ForV^IV in pH 7 buffer, both catechol and Mm-1 formed complexeswith V^IV ions, and no redox productswere found. For V^V in pH 2 buffer, both catechol andMm-1 were oxidized by V^V ions. RoomtemperatureEPR qualitatively showed that Mm-1 in pH 2 buffer reducedV^V ions to free V^IV ions. ForV^V in pH 7buffer, Mm-1 was oxidized by V^V ions and formedV^IV complexes. At higher concentrations, theV^IVcomplexes 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 acolorimetric assayfor V^III, we found that reactions between Mm-1 andV^V or V^IV ions in pH 7 buffer clearly did notgenerateappreciable quantities of V^III products. Thus, thecolorimetric V^III assay resolved the issue ofV^III productformation 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-vanadiumchemistry and identify conditions whichpromote complexation and/or redox reactions invitro.