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FTIR Spectroscopy of <strong>Calcium</strong>-<strong>Binding</strong> <strong>Protein</strong>s 57<br />

5<br />

Fourier Transform Infrared Spectroscopy<br />

of <strong>Calcium</strong>-<strong>Binding</strong> <strong>Protein</strong>s<br />

Heinz Fabian and Hans J. Vogel<br />

1. Introduction<br />

Infrared spectroscopy measures absorptions of vibrating molecules and yields<br />

information about molecular structure and structural interactions. Over the last<br />

two decades, the infrared technique has emerged as a very useful tool for examining<br />

protein conformation as a result of the increase in energy throughput, achievable<br />

signal-to-noise ratio, wavenumber accuracy, and data aquisition rates that<br />

came with the development of Fourier transform infrared (FTIR) spectrometers.<br />

High-quality infrared spectra can now rapidly be aquired and require only relatively<br />

small amounts of protein. The size of the protein or the nature of the<br />

environment does not limit the application of FTIR spectroscopy. Importantly,<br />

measurements of proteins in aqueous solution are almost routine now. Furthermore,<br />

the process of obtaining structural information is not restricted to a static<br />

picture, but can also be achieved in real time by applying time-resolved infrared<br />

techniques. The effects of environmental factors, point mutations, or ligand binding<br />

on the structure of the proteins can be examined with high sensitivity by<br />

using peptide backbone and side-chain infrared bands as conformation-sensitive<br />

monitors. In combination with isotope labeling, the technique also permits<br />

the study of protein–protein or protein–peptide interactions.<br />

2. Materials<br />

2.1. FTIR Spectrometer<br />

Spectrometers required for measuring high-quality spectra of proteins in the<br />

midinfrared region are available from a variety of manufacturers. These<br />

research-grade instruments offer a spectral resolution of better than 1 cm –1 and<br />

From: Methods in Molecular Biology, vol. 173:<br />

<strong>Calcium</strong>-<strong>Binding</strong> <strong>Protein</strong> <strong>Protocols</strong>, Vol. 2: Methods and Techniques<br />

Edited by: H. J. Vogel © Humana Press Inc., Totowa, NJ<br />

57

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