Mn(II)‐EPR measurements of cation binding by aequorin

Marvin D. KEMPLE, Michael L. LOVEJOY, Bruce D. RAY, Franklyn G. PRENDERGAST, B. D. NAGESWARA RAO

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Abstract

Cation binding at 5°C by aequorin, a bioluminescent protein from the jellyfish Aequorea victoria, was examined by means of Mn(II) EPR. The bioluminescence of aequorin is triggered by Ca(II), as well as by trivalent lanthanides, and is inhibited by Mg(II) and Mn(II). Three EF‐hand Ca(II)‐binding domains have been identified in the aequorin amino acid sequence. In the work reported here, active native aequorin was found to have a single tight binding site for Mn(II) with an association constant of 0.566 μM−1. Ca(II) and La(III) competed for the Mn(II) site with association constants of 1.92 μM−1 and 1.38 μM−1, respectively. The affinity of Ca(II) and La(III) for their two other (presumed) sites on aequorin was an order of magnitude less than their affinity for the Mn(II) site. Mg(II) competed for the Mn(II) site as well but with a much smaller association constant of 0.0109 μM−1. Ca(II)‐independent discharged aequorin did not bind Mn(II) to a significant degree. Conjectures on the location of the Mn(II) site in the aequorin amino acid sequence and on the relationship between the binding parameters of the cations and their influence on aequorin activity are given.

Original languageEnglish (US)
Pages (from-to)131-135
Number of pages5
JournalEuropean Journal of Biochemistry
Volume187
Issue number1
DOIs
StatePublished - Jan 1990

ASJC Scopus subject areas

  • Biochemistry

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    KEMPLE, M. D., LOVEJOY, M. L., RAY, B. D., PRENDERGAST, F. G., & NAGESWARA RAO, B. D. (1990). Mn(II)‐EPR measurements of cation binding by aequorin. European Journal of Biochemistry, 187(1), 131-135. https://doi.org/10.1111/j.1432-1033.1990.tb15286.x