Calcium Ion Binding to Pancreatic Phospholipase A2 and Its Zymogen: A 43Ca NMR Study

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Abstract

Calcium ion binding to phospholipase A2 and its zymogen has been studied by 43Ca NMR. The temperature dependence of the band shape of the calcium-43 NMR signal has been used to calculate the calcium ion exchange rate. The on-rate was calculated to be 5 × 106 M-1 s-1, which is 2 orders of magnitude less than the diffusion limit of the hydrated Ca2+ ion in water. The 43Ca quadrupole coupling constant for calcium ions bound to phospholipase, χ = 1.4 MHz, is significantly larger than those found for EF-hand proteins, indicating a less symmetric site. For prophospholipase A2, we found χ = 0.8 MHz, indicating a calcium binding site, which is somewhat more symmetric than the EF-hand sites. The dependence of the Ca NMR band shape on the calcium ion concentration showed that there are two cation binding sites on the phospholipase A2 molecule: K1 = 4 × 103 M-1 and K2 = 20 M. The strong site was found to be affected by a pKa = 6.5 and the weak site by pKa = 4.5.

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Authors
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  • Lund University
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Theoretical Chemistry
Original languageEnglish
Pages (from-to)2387-2392
Number of pages6
JournalBiochemistry
Volume23
Issue number11
Publication statusPublished - 1984 Jan 1
Publication categoryResearch
Peer-reviewedYes