Calcium binding to bone γ-carboxyglutamic acid protein from calf studied by 43Ca NMR

Authors


  • Note. The rotational correlation time (τrotc) of BGP can be estimated to approximately 2 ns at 20°C from the Debye-Stokes-Einstein equation [25]. We are thus able to determine an upper limit of ωτc in our experiments: ωτ2 < 0.22 (ω= 1.078 · 108 s−1 and τc <2 · 10−9 s).

Correspondence to M. Svärd, Avdelningarna för Fysikalisk Kemi 1 och 2, Kemicentrum, Lunds Universitet, Box 124, S-22100 Lund, Sweden

Abstract

Calcium binding to bone γ-carboxyglutamic acid protein (BGB) from calf has been studied using 43Ca NMR. The temperature dependence of the 43Ca NMR signal has been used to calculate the calcium ion exchange rate, koff. The dependence of the 43Ca NMR band shape on the [Ca2+]/[BGP] ratio fits well to a chemical equilibrium model having a single Ca2+ -binding site with an association constant in the range of 5 × 103–1 × 105 M−1. The pH dependence of the 43Ca NMR line-width shows a single apparent pKa value of 5.1.

Abbreviations
Gla

γ-carboxyglutamic acid

BGP

bone Gla protein, osteocalcin

HPLC

high-performance liquid chromatography

SDS

sodium dodecyl sulphate